Field of Science

Zerconids

Slide-mounted male of Zercon gurensis, copyright Holger Müller.


The animal depicted above is a mite of the Zerconidae, one of the numerous families in the major mite clade known as the Mesostigmata. This family is mostly found in soil habitats such as leaf litter, mosses, decaying vegetation, or occasionally in animal nests (Lindquist et al. 2009). The zerconids are restricted to the Northern Hemisphere and are most diverse in temperate to Arctic regions; those species found in tropical parts of the world are restricted to high altitudes away from the hot lowlands (Ujvári 2012). Like many other Mesostigmata, they have the dorsal surface of the body mostly covered by shields of hardened cuticle. In most zerconids, separate shields cover the front (podonotal) and rear (opisthonotal) sections of the dorsum; the opisthonotal shield wraps around the rear margin of the mite and forms a continuous unit with the ventrianal shield that usually protects most of the underside of the mite behind the legs. Among the most noticeable features of the zerconids are two pairs of large openings near the rear of the opisthonotal shield (the four orange-segment-like structures in the photo above). These represent the openings of secretory glands, but I don't know if it has been established just what they're secreting; comparable structures in other mites may secrete pheromones, or defensive chemicals, or oils that prevent debris from sticking to the body. Other features of the zerconids include slender, relatively simple chelicerae that lack the modifications seen in the males of some other Mesostigmata, and peritremes (grooves on the underside of the body that channel air to the openings of the respiratory stigmata) that are relatively short. These peritremes are longer in zerconid nymphs, but become shortened when the mite moults to maturity.

Zerconids are another of those mite groups where the vast majority of what has been written about them relates to their basic taxonomy, with little yet known about their natural history. Several genera of zerconids are recognised, distinguished by features such as the shape of the body's various shields and the appearance of various setae. The form of their chelicerae indicates that zerconids are predatory like many other Mesostigmata. Because they are mostly found at ground level rather than on vegetation they have not attracted the economic interest of other predatory mites, but those few species that have been observed feeding were chowing down on nematodes. Mating does not appear to have been directly observed in zerconids, but again their anatomy and comparison with other mesostigs allows us to infer that the male fertilises the female by using his chelicerae to pass a spermatophore from his own genital opening on the underside of the body between the legs to hers. Where she then lays her eggs, and how her offspring spend their time to maturity, seem to be questions still awaiting an answer.

REFERENCES

Lindquist, E. E., G. W. Krantz & D. E. Walter. 2009. Order Mesostigmata. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 124–232. Texas Tech University Press.

Ujvári, Z. 2012. Draconizercon punctatus gen. et sp. nov., a peculiar zerconid mite (Acari: Mesostigmata: Zerconidae) from Taiwan. Opusc. Zool. Budapest 43 (1): 79–87.

Midges of the Macabre

In a recent post, I commented that derived members of an insect 'order' could sometimes be all but unrecognisable as belonging to that order. Take a look at this:

Miastor sp., copyright Charles Olsen.


Believe it or not, sitting in the middle of that photo is a fully reproductively mature insect (I'm not so sure about the maturity of the other individuals). In fact, it's a fully mature fly. Miastor is a genus of midges found living in rotting wood or fungal fruiting bodies. Members of this genus are found worldwide; I believe that several species are recognised, but distinguishing the individual species is extremely difficult. Miastor exhibit what is called paedogenesis: they can become reproductively mature while still in the larval state. They are not the only genus of the family Cecidomyiidae to exhibit this process; another such genus, Oligarces, is found in similar habitats. Miastor is probably the best known such genus, in part because it has been cultured for study in the laboratory, and in part because of the decidedly macabre way in which its paedogenesis plays out.

Each paedogenetic Miastor larva develops several eggs within its ovaries (generally four to ten or more—Harris 1923). No males are involved in this process: the larvae are parthenogenetic as well as paedogenetic. These eggs hatch while still inside their mother, after which the daughter larvae are nourished by the mother's own tissues. Eventually, the daughters are not born so much as they escape. In the words of Quammen (1985), "While the food lasts, while opportunity endures, no Miastor female can live to adulthood without dying of motherhood". But karma still seems to have its place, because by the time the daughter larvae escape they carry their own fate within them: they emerge with their own eggs already developing inside them.

Metamorphosed male Miastor metraloas, copyright John Plakidas.


In this way, a Miastor colony can go through an entire generation in as little time as two weeks, until changing conditions (such as exhaustion of food supplies, or a change in season) induce a change in tack. Larvae are produced that do not reproduce paedogenetically in the way that their mothers did, but instead pupate in the usual way to emerge as more ordinarily formed midges, both males and females. As with another paedogenetic insect that has already been featured on this site, the beetle Micromalthus debilis, these metamorphosing larvae can be readily distinguished from paedogenetic larvae. Not only do they not produce the precocious reproductive organs of their fellows, but they have visible imaginal discs (the clumps of tissue that develop into adult structures during metamorphosis), and have eyes that are clearly separated on top rather than touching as in paedogenetic individuals (Harris 1923). After the mature adult midges emerge from their pupae, they can disperse in search of new habitats, seeking food for their offspring and mates for themselves in order to begin the cycle again.

REFERENCES

Harris, R. G. 1923. Occurrence, life-cycle, and maintenance under artificial conditions, of Miastor. Psyche 30 (3–4): 95–101.

Quammen, D. 1985. Natural Acts. Schocken Books.

The Mongolian Death Worm

This would have been a comment on a recent post by Darren Naish at Tetrapod Zoology on the behaviour of amphisbaenians, but the commenting system they have at Scientific American these days means that any comment on a post more than a couple of days old will never be seen by anyone. As such, I'm posting it up here:

PhilJTerry's comment in response to Darren's post: "As I love introducing cryptozoology into the conversation wherever possible - are Amphisbaenians a likely influence for the Mongolian Death Worm? Can they live in desert environments?"

Image from National Geographic.


For those not already aware, the "Mongolian death worm" or "olgoi-khorkhoi" is a supposedly incredibly dangerous animal found in the deserts of Mongolia. It's first mention in Western literature came in Roy Chapman Andrew's (1926) On the Trail of Ancient Man. Andrews heard about the animal in a meeting with Mongolian officials:

Then the Premier asked that, if it were possible, I should capture for the Mongolian government a specimen of the allergorhai-horhai. I doubt whether any of my scientific readers can identify this animal. I could, because I had heard of it often. None of those present ever had seen the creature, but they all firmly believed in its existence and described it minutely. It is shaped like a sausage about two feet long, has no head nor legs and is so poisonous that merely to touch it means instant death. It lives in the most desolate parts of the Gobi Desert, whither we were going. To the Mongols it seems to be what the dragon is to the Chinese. The Premier said that, although he had never seen it himself, he knew a man who had and had lived to tell the tale. Then a Cabinet Minister stated that "the cousin of his late wife's sister" had also seen it. I promised to produce the allergorhai-horhai if we chanced to cross its path, and explained how it could be seized by means of long steel collecting forceps; moreover, I could wear dark glasses, so that the disastrous effects of even looking at so poisonous a creature would be neutralized. The meeting adjourned with the best of feeling; for we had a common interest in capturing the allergorhai-horhai.


Since then, there have been a number of expeditions have been conducted in search of the Premier's "allergorhai-horhai"; all have come up fruitless. Various opinions have been expressed as to what the stories may have been based on, with the most popular suggestions being some sort of reptile (Darren says in his response to the above comment on the original post that he "could buy that the stories are based on exaggerated tales of erycine boas or something"). For my part, I suspect that the question of the 'original identity' of the Mongolian death worm may be a futile one. When I first heard Andrews' account, I was not reminded of an amphisbaenian or a boa; I was immediately put in mind of a drop bear.


I feel almost certain that Andrews was being told a local tall tale, a popular joke at the expense of visiting travellers. The nature of Andrews' response to the officials suggests that he was in on the joke and more than happy to play his part in communicating it. Admittedly, other accounts of the Mongolian death worm have been recorded at more recent dates. And in the same way, I've never seen a drop bear myself, but I can assure you that my cousin did once and got the fright of his life. Be careful. They're out there.

Scurvy and Cress

Without the subject of today's post, it's just possible that my home country of New Zealand could have had quite a different history. Sometimes, one shouldn't overlook the importance of cress.

Pepperwort Lepidium heterophyllum, copyright Anne Burgess.


Lepidium is a genus of herbs and subshrubs belonging to the Brassicaceae, the same family as cabbages, radishes and cauliflowers. The genus is found worldwide, and more than 150 species have been recognised to date. The fruit is a type of dry capsule called a silicle which is usually dehiscent (one subgroup of Lepidium, previously separated as the genus Cardaria, has indehiscent fruit), with strongly keeled or winged valves, and contains a single pendulous seed in each locule. The seeds are usually copiously covered in mucilage (Mummenhoff et al. 2001). Like other members of the Brassicaceae, Lepidium has not been overlooked for culinary uses. Leaves and stems of number of species in the genus, such as garden cress Lepidium sativum and dittander Lepidium latifolium, are used as pot or salad herbs. A South American species, maca Lepidium meyenii, is grown as a root vegetable.

Because of its wide distribution, some early authors suggested that Lepidium was a very ancient genus whose members had diverged with the break-up of the Mesozoic supercontinents. However, more recent phylogenetic analyses (Mummenhoff et al. 2001) have suggested just the opposite: the crown group of Lepidium may have originated in the Mediterranean-Central Asian region little more than two million years ago. The mucilaginous seeds of many species become sticky when damp, and can easily be carried long distances adhered to birds' feet and other such dispersal agents. Perhaps the most dramatic suggestion of intercontinental dispersal in the genus involves a clade of species found in Australia and New Zealand that phylogenetic analysis suggests originated via hybridisation between two divergent species—with one parent being native to South Africa and the other to California (Mummenhoff et al. 2004).

Cook's scurvy grass Lepidium oleraceum, copyright Andrea Brandon.


It was one of the members of the latter clade that played a small but significant role in New Zealand history. Lepidium oleraceum is an endemic New Zealand species that was once found growing over much of the country. It is commonly known as 'Cook's scurvy grass', because Captain James Cook was able to collect it while surveying New Zealand to provide vitamin C to stave off the scurvy that could have otherwise devastated his crew. Sadly, this once common plant is now extremely rare: the disappearance of mainland-nesting seabirds means that they are no longer around to provide the guano-enriched soils on which this plant thrived. It also proved extremely palatable to introduced herbivores. As a result, Cook's scurvy grass is now almost exclusively found on small offshore islets.

REFERENCES

Mummenhoff, K., H. Brüggemann & J. L. Bowman. 2001. Chloroplast DNA phylogeny and biogeography of Lepidium (Brassicaceae). American Journal of Botany 88 (11): 2051–2063.

Mummenhoff, K., P. Linder, N. Friesen, J. L. Bowman, J.-Y. Lee & A. Franzke. 2004. Molecular evidence for bicontinental hybridogenous genomic constitution in Lepidium sensu stricto (Brassicaceae) species from Australia and New Zealand. American Journal of Botany 91 (2): 254–261.

Linnaeus' Infernal Fury

The starting point of modern zoological nomenclature (Clerck notwithstanding) has been established as the tenth edition of Linnaeus' Systema Naturae, published in 1758. Linnaeus divided the animal kingdom between six classes, with vertebrates making up four (Mammalia, Aves, Amphibia and Pisces) and invertebrates assigned to just two. One of these, Insecta, essentially corresponded to modern arthropods, and all other invertebrates were included in the class Vermes, 'worms'. Linnaeus' concept and arrangement of Vermes bears little resemblance to anything that exists in modern zoological classifications; with the study of invertebrate anatomy still in its absolute infancy, he was largely classifying animals based on their overall external appearance alone. One of Linnaeus' orders of Vermes, the 'Intestina', defined as 'simple, shell-less and limb-less', included animals now classified as annelids, nematodes, molluscs and even a chordate (the hagfish Myxine glutinosa). It also included a species whose identity would be debated for the next several decades: the 'infernal fury', Furia infernalis.

A reconstruction of Furia infernalis, from Piter Kehoma Boll.


Furia infernalis was described by Linnaeus as "Corpus filiforme, continuum, aequale, utrinque ciliatum: aculeis reflexis corpori appressis" ('body thread-like, continuous, uniform, ciliated on both sides with reflexed spinules appressed to the body'). It was found in marshes of southern Sweden and Finland. Linnaeus went on to record that F. infernalis was, "Pessima omnium, ex aethere decidua in corpora animalium, ea momento citius penetrat, intra horae quadrantem dolore atrocissimo occidit": the 'worst of all, falling from the sky onto the bodies of animals, into which it rapidly penetrates within a moment, striking [the victim] down with the most atrocious pain within quarter of an hour'. Linnaeus had good reason to highlight this animal's unpleasantness: he had been attacked by one himself when collecting botanical specimens in 1728, and barely escaped the resulting ailment with his life. A more detailed description of "der Höllenwurm" was compiled by Jördens (1802): it was a very slender worm, about the length of a nail, of a pale yellow or fleshy colour (other authors described it as greyish), with one end black. It climbed up standing vegetation, from whence it was carried by the breeze onto the exposed skin of humans and animals into which it rapidly burrowed. For victims, the first sign of its presence was usually a sudden pain in the afflicted spot, like the stab of a needle, and a small black spot marking the worm's entry point. A violent itching followed that developed into severe and extensive inflammation, often accompanied by fever; in the majority of cases, the affliction was so violent that the victim was dead within a matter of days if immediate action was not taken. If applied quickly enough, the worm could sometimes be drawn out with a poultice of fresh cheese curds. Otherwise, treatment required the careful dissection of the worms from between the muscle tissue into which they had entered, a process that (considering the surgical facilities available at the time) must have nearly as hazardous as the original infection.

As can be imagined, the attacks of this animal were greatly feared. In 1823–1824, an epidemic of Furia attacks spread through herds of livestock in Swedish and Finnish Lapland; thousands of head of reindeer perished, as well as countless cattle and sheep. Scavengers such as wolves feeding on the carcasses themselves sickened and died. One account from the time involves a young woman who was shearing wool from a recently deceased sheep (on a waste not, want not principle, I suppose) when she felt the tell-tale sting on a knuckle. Her life was saved by her master who was working nearby, when he quickly chopped off the affected finger with an axe. So great was the devastation that Norway, which had hitherto been free of the worm, passed an edict banning the import of animal furs from affected areas (Brooke 1827).

There were some, however, who greeted the description of Furia infernalis with skepticism. The idea of a tiny worm that somehow flew through the air and caused almost instantaneous mortality seemed fantastic. Even more problematic was the dearth of specimens. Many had seen the wounds caused by the worm and observed its effects; very few had seen the worm itself. Linnaeus himself had only seen a single, very poorly preserved specimen submitted to him by a church pastor. Most of the details about the worm's supposed appearance came from a single source, an article written by Solander, a student of Linnaeus'. The Academy of Sciences at Stockholm, naturally keen to discover all they could about such a scourge afflicting their country, offered generous rewards to anyone who could procure them a genuine specimen; no such specimen was forthcoming. Eventually, a consensus was reached: the worm Furia infernalis was an entirely fabulous animal, with no place in the annals of physical zoology. By 1827, notwithstanding the epidemic of only a few years previously, Brooke was able to comment that one could quite easily accept that something had affected the supposed victims of Furia without presuming that that something had to be the Furia itself. Even Linnaeus eventually came to accept that his inclusion of Furia in the Systema Naturae had been an error.

That Furia infernalis never existed outside the realms of fantasy remains the accepted wisdom to this day. But in that case, what did afflict Linnaeus and other unfortunates wandering the marshes of Sweden in the early 1700s? One thing that struck me was how much I was reminded of the more recent phenomenon here in Australia of 'white-tailed spider bites'. In recent decades, many people (including many medical professionals) have attributed serious ulcerative skin lesions, sometimes so serious that treatments such as skin grafts are required, to the bite of white-tailed spiders Lampona spp., common ground-running spiders often encountered near human dwellings. The actual evidence linking white-tailed spiders to such injuries is minimal; indeed, a clinical survey of 130 confirmed white-tail bites by Isbister & Gray (2003) found not a single incidence of one leading to ulceration. In both the 'Furia attacks' and the 'white-tailed spider bites', it seems likely that the primary culprit is bacterial infections resulting from opportunistic pathogens such as Streptococcus and Staphylococcus species. The initial wound may indeed have been caused by something like an animal bite or sting, or for that matter a splinter or pin-prick. Germ theory would not become widely accepted until the mid- to late 1800s; when Linnaeus compiled the Systema Naturae, flying worms probably seemed as good an explanation as any. The first 'attack' recorded by Furia victims may have simply been the first moment they noticed the infection's symptoms. And the 'worms' dissected out of advanced victims? Personally, I'm inclined to suspect that they may have been small pieces of tissue from the unfortunate sufferers themselves.

The exact causes of the 1823 epidemic are probably lost to history. Brooke (1827) stated that faculty at the Stockholm academy "had been led to consider the disorder by which [the reindeer] were attacked as a particular variety of hydrophobia". He also mentioned another possibility: reindeer were known to be vulnerable to inflammation of the brain, and dissections of the brains of deer killed by this condition sometimes revealed the presence of "a small vesicular worm". We can now recognise these vesicles as the cysts of hydatid tapeworms, which can hatch to cause tapeworm infections in any predator that eats the flesh of their host. So perhaps the 1823 epidemic was caused by a worm after all—just not the worm that was blamed.

REFERENCES

Brooke, A. de C. 1827. A Winter in Lapland and Sweden, with various observations relating to Finmark and its inhabitants; made during a residence at Hammerfest, near the North Cape. John Murray: London.

Isbister, G. K., & M. R. Gray. 2003. White-tail spider bite: a prospective study of 130 definite bites by Lampona species. Medical Journal of Australia 179: 199–202.

Jördens, J. H. 1802. Entomologie und Helminthologie des Menschlichen Körpers, oder Beschreibung und Abbildung der Bewohner und Feinde desselben unter den Insekten und Würmern vol. 2. Gottfried Adolph Grau: Hof.

Linnaeus, C. 1758. Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis 10th ed., revised, vol 1. Laurentius Salvius: Copehagen.

Two New Insect Orders?

When a new species of insect is described as being distinct enough to represent a new order, it's kind of a big deal. So it certainly caught my attention over the past year when, not one, but two species from Cretaceous Burmese amber were considered worthy of the honour. Now, I'm going to be up front here and say that, while both are very interesting specimens, in both cases I think that the 'new order' label may be a trifle overblown. What's interesting to me is that my reasons for thinking so are different for both. Let's take a look, shall we?

Lateral and dorsal views of holotype of Alienopterus brachyelytrus, from Bai et al. (2016). Pink scale bar = 1 mm.


The first was published in March of last year by Bai et al. (2016) under the name of Alienopterus brachyelytrus. In overall appearance, Alienopterus resembled a long-legged cockroach, but with the head clearly visible instead of hidden by the pronotum in the cockroach manner. The head would have been mobile and capable of being turned in the manner of a modern cockroach or mantis. The forewings were hardened and reduced to small pads covering only the base of the hind wings, which retained their full length. The femora of the front legs bore a pair of dense rows of setae on their underside, and Bai et al. suggested that Alienopterus may have used these setae to help it grab prey.

A phylogenetic analysis of Alienopterus placed it together with the modern cockroaches and mantids, specifically as the sister group to the latter. Because Alienopterus lacked the primary distinguishing features of a mantis (such as the spined raptorial forelegs), and because of its distinctive wing morphology, Bai et al. made it the type and only species of a new order, the Alienoptera. But there are a number of reasons why I find this designation problematic. It is generally agreed these days that cockroaches and mantids (and termites) together form a clade known as the Dictyoptera. Many people have an idea that cockroaches are one of the oldest living groups of insects, having supposedly been around for hundreds of millions of years. But modern cockroaches and mantids only diverged sometime during the Jurassic and Cretaceous; earlier members of the Dictyoptera were cockroach-like, certainly, but they were just as close to mantids as to cockroaches, and also had features very distinct from either. If we are to recognise a distinct 'order' for Alienopterus purely on phylogenetic grounds, then we would also have accept several separate 'orders' for each of the various lineages of stem-dictyopterans. And as distinctive as Alienopterus is morphologically, it is not the only (or even the most) unusual member of the Dictyoptera. This is, after all, the lineage that has given the termites with their wood-chomping biology and baroque caste system, beetle-like taxa with full-on elytra, and active leapers like the Jurassic Skok svaba or the modern Saltoblattella montistabularis.

There is a definite paradox at play here. On the one hand, the question of which lineages get designated 'orders' is completely arbitrary because there is no formal definition for an 'order' except that it is a taxon that is somehow more significant than a 'family' (itself a completely arbitrary level). From that perspective, there is no inherent reason why the Dictyoptera should not get divided between any number of orders. But on the other hand, the concept of 'order' has a certain cultural cachet. 'Orders' are kind of the base units of entomology: the first thing that any student of entomology is likely to do is learn to distinguish between the various insect orders. Labelling a particular taxon an 'order' is a statement of value; it says that that taxon is somehow fundamentally important in a way that other taxa are not. And while, again, Alienopterus is a very interesting animal in terms of what it can potentially tell us about cockroach-mantis relationships, it is hard to see how it can be called 'fundamental'. There have been extinct 'orders' recognised from the fossil record, such as the Palaeodictyoptera, but such taxa represent notable radiations. With only a single known species, referring to Bai et al.'s taxon as 'Alienoptera' tells us little more than calling it an unplaced species within the Dictyoptera.

Various views of Aethiocarenus burmanicus from Poinar & Brown (2016).


The other new 'order' made its appearance in December, when Poinar & Brown (2017) published Aethiocarenus burmanicus (if you're confused about the date, it reflects the difference between the online and print publication). This was a very odd little insect: a flattened and wingless yet long-legged animal with long antennae. The most distinctive feature of Aethiocarenus is its head, which is globular with great bulging eyes and placed on a narrow neck. Poinar & Brown suggest that it may have made its living hunting in confined spaces, such as crevices in bark or among epiphytes. Because of its highly distinctive appearance from any other known insect, Poinar & Brown placed it in its own new order, the Aethiocarenodea.

In this case, my issue with the establishment of a new 'order' is that it is essentially a statement of ignorance. As distinctive as Aethiocarenus is, there are many equally unusual-looking insects that are not placed in their own 'order'—particularly among wingless forms that can get up to all sorts of freakiness. The overall 'jizz' of Aethiocarenus, particularly the distinct cerci, suggest that its affinities probably lie somewhere within the Polyneoptera, the group of insects including such forms as cockroaches, grasshoppers and stoneflies. Within other polyneopteran orders, a novice entomologist would be hard-pressed to recognise a sandgroper as a grasshopper, or the Javan cave-dweller Arixenia esau as an earwig. Similarly, without a formal analysis it is difficult to exclude the possibility that Aethiocarenus represents a kooky member of some already recognised order. And again, with only one known species, recognition of an 'order' Aethiocarenodea tells us little more than recognition of an unplaced Aethiocarenus.

REFERENCES

Bai, M., R. G. Beutel, K.-D. Klass, W. Zhang, X. Yang & B. Wipfler. 2016. Alienoptera—a new insect order in the roach-mantodean twilight zone. Gondwana Research 39: 317–326.

Poinar, G., Jr & A. E. Brown. 2017. An exotic insect Aethiocarenus burmanicus gen. et sp. nov. (Aethiocarenodea ord. nov., Aethiocarenidae fam. nov.) from mid-Cretaceous Myanmar amber. Cretaceous Research 72: 100–104.

Screech Owls

Eastern screech owl Megascops asio emerging from a nest-hole, copyright Zach.


For many people, owls are a group of birds known more by reputation than by encounter. Their nocturnal lifestyles and often cryptic habits make them rarely seen, and their diversity is often little appreciated. But despite being commonly referred to as a single homogeneity, owls actually come in a whole range of shapes and forms.

Megascops, the screech owls, is a genus of more than twenty species found over most of the Americas, though they are less diverse in North America than in the remainder of their range. They are also notably absent from the Caribbean; a single species from that region assigned to this genus, the Puerto Rican screech owl Megascops nudipes, was found in a recent phylogenetic study (Dantas et al. 2016) to be closer to the flammulated owl Psiloscops flammeolus of North America and may require reclassification. Despite what one might presume from the genus name alone, species of Megascops are small owls, around 20–25 cm in length. They have prominent grey facial discs and distinctly developed ear tufts. When disturbed, they will freeze upright in place with the ear tufts raised and the eyes almost closed; this, together with their broken brown or grey coloration, allows them to pass as an unremarkable piece of the tree they are sitting on. The most distinctive characteristic of the genus is their song, produced by members of both sexes, which comprises a rapid trill of several closely placed notes. The exact pattern of the song varies from species to species, and is commonly the most reliable method of telling each species apart (though, just for the sake of perversity, individuals that live in sympatry with members of another species may engage in mimicry). The species are otherwise often difficult to distinguish by external features alone. Just to confuse matters further, many (but not all) species of screech owl exhibit distinct colour morphs, with one morph being predominantly grey and the other rufous, that might be mistaken by the unwary for distinct species.

Pair of tropical screech owls Megascops choliba exhibiting distinct colour morphs, from Nucleo de Fauna.


As is not uncommon for owls, the majority of Megascops species are poorly known from a natural history perspective. Gehlbach & Stoleson (2010) provided a review of one of the North American species, the western screech-owl Megascops kenniscottii, that is probably typical of the genus. The diet of screech owls (like other small owls) is dominated by insects, with small vertebrates making up less than a fifth of their regular daily intake. Nesting takes place in holes in trees; nesting holes are claimed and defended by the male, who advertises its (and his) availability to females via the medium of song. Females respond to the males' advertisements by singing in reply, and pairs of owls will also respond defensively to songs from other owls nearby. The series of calls and responses in densely populated regions may develop into a full chorus of acknowledgements and challenges. Incubation of the clutch of about four eggs (which in the western screech owl is usually laid around late March–early April) is done solely by the female with the eggs taking about a month to hatch. The male collects food for her and the newly hatched chicks; after the chicks begin to fledge, both parents hunt for food for them.

The majority of screech owl species are not considered threatened conservation-wise though some of the more localised species may be vulnerable to habitat loss. Screech owls are reasonably tolerant of human activity and will even live and nest in suburban regions. They usually only disappear from a region once it becomes completely urbanised.

REFERENCES

Dantas, S. M., J. D. Weckstein, J. M. Bates, N. K. Krabbe, C. D. Cadena, M. B. Robbins, E. Valderrama & A. Aleixo. 2016. Molecular systematics of the new world screech-owls (Megascops: Aves, Strigidae): biogeographic and taxonomic implications. Molecular Phylogenetics and Evolution 94: 626–634.

Gehlbach, F. R., & S. H. Stoleson. 2010. Western screech-owl (Megascops kennicottii). In: Cartron, J.-L. (ed.) Raptors of New Mexico pp. 511–523. University of New Mexico Press: Albuquerque.