Field of Science

A Seclusion of Embioptera

A work colleague and I got into a conversation a while ago about collective nouns, and of course that eventually got onto the question of making up appropriate terms for groups of animals that currently lack collective nouns. One suggestion that I came up with that I still rather like the sound of was a "seclusion of embiopterans". From now on, I urge you to use the term when discussing embiopterans.

If through some bizarre oversight you haven't regularly found yourself discussing embiopterans, then you really should be. Also known as webspinners or embiids, embiopterans are one of the definite contenders for the total of world's coolest insects. I have personally come across a specimen in the wild just once that I found clinging to a piece of bark I pulled off its tree - unfortunately, I have to admit, no-one around me quite got what I was getting so excited about.

Webspinners are small insects that live in silken galleries they build in secluded areas such as under bark or rocks (the picture above from the homepage of Janice Edgerly-Rooks shows a female webspinner peeping out of its home). There is something of an esoteric contention about what exactly the correct name for the webspinner order should be - Embioptera, Embiidina or Embiodea all can be found. I'm going to stick with Embioptera for no good reason. The name means "lively wings" and is wildly inappropriate - webspinners are not noticeably lively, and more often than not lack wings (females are invariably wingless, males can sometimes be). It has been suggested that the name refers to the flicking movement of the male wings. The wings of male webspinners have large blood sinuses developed from the veins that are pumped full of haemolymph to make the wings rigid when they fly. When the haemolymph is drained from the sinuses, the wings become limp and floppy, able to move in whatever direction is required to let the male crawl through a female's silk nest, even bending forward over the head if the male goes into reverse.

Webspinners are often referred to as semi-social and females may share inter-connected galleries. Females also show a high level of parental care. However, females will not show any care for the young of others, and social interactions between females should probably be regarded as opportunistic rather than required (Grimaldi & Engel, 2005). The female and juvenile webspinners emerge from their silken palaces at night to feed on vegetation and detritus. Adult males, on the other hand, do not feed.

The webspinner's silk glands are located along the edge of the third segment of the forelimb tarsus, which is noticeable broadened as shown in the diagram above from BugNetMAP. The German name for embiopterans, "tarsenspinner", is therefore entirely apropos. The stunning "Life in the Undergrowth" series that I've had cause to mention before included spectacular footage of a webspinner constructing its silken fortress, waving its forelimbs in front of itself in a motion that can only be described as "wax on, wax off". So impermeable is the resulting wall that the spinner must actually cut through it with its mandibles in order to drink from water drops lying on the surface if it is not to dry up completely.


  1. yay! Only ever foud a single one myself. Or rather, my dad did, in our front brick wall he was knocking down. Very surprising.

  2. How about "an orgy of bedbugs" and "an invasion of strepsipterans"?

  3. Leaving aside the point that, in light of their general abundance, a collective noun for strepsipterans would have to be the most useless term in the English language, I think the most appropriate term for a group of Strepsiptera is a 'queenage'. I'll have to do a post on Strepsiptera at some point.

  4. Cool post! I haven't heard of this group of insects before. Why do insect biologists name body parts like vertebrate biologists do (i.e. tibia from the last picture) and not like crustacean biologists? For instance, the leg segments are merus, ischium, propodus, carpus and dactylus. Since insects and crustaceans are sister taxa, shouldn't their anatomical terminology be homologous?

    Also, where do embiopterans fit in insect phylogeny? Who are their close relatives?

  5. Why do insect biologists name body parts like vertebrate biologists do... and not like crustacean biologists?

    That's a bloody good question - I'd never actually clicked that crustaceans had different terminology! Arachnids use the same terminology as insects, so I would guess it's a historical artifact of the separation between marine and terrestrial terminology. From the base of the leg outwards, the segments are coxa, trochanter, femur, patella, tibia, tarsus, apotele. I'm not that familiar with work on homologies between different arthropod classes, but it's a pretty contentious subject and I wouldn't assume that, say, the tibia of an insect was necessarily evolutionarily homologous with the tibia of an arachnid.

    Embiopterans are part of the Polyneoptera, the basal group of Neoptera (the clade of all living insects except dragonflies and mayflies, distinguished by being able to fold the wings back). Polyneopterans include cockroaches, grasshoppers, stoneflies and a number of smaller orders. Though there is a certain similarity in superficial appearance between the polyneopteran orders, we pretty much don't know at present whether they form a clade or a paraphyletic grade with respect to the clade formed by Paraneoptera (bugs and allies) + Holometabola (insect with larval and pupal stages). Polyneopterans have a fairly primitive development (except for the absence of wings, nymphs are little different from adults) compared to holometabolans or paraneopterans (which don't have the pupal stage of holometabolans, but do have nymphs that are pretty distinct from the adults).

    Relationships within polyneopterans are even more uncertain. Terry & Whiting (2005) supported embiopterans as sister to phasmids (stick-insects), with that clade in turn sister to Orthoptera (grasshoppers and crickets), but this will not be the last word on the subject.

  6. Insects are an absolute mess in general. But I am curious now as to why the whole terminology thing. Because arachnids and insects are rather far apart. The Chelicerata I would imagine could be sister to the crustacean + insect clade. But Insects and crusties are supposedly very closely related. The first segment of the crustacean limb is also called the coxa but then its all different [3)ischium, 4) merus, 5) propodus, 6) carpus, 7) dactyl - I believe the 2nd segment is fused with the coxa]. Maybe we should write a paper describing the homology and switch it to crustacean terminology lol

  7. Between the arachnids and the insects (and probably the myriapods too), we terrestrial types have you marine types well out-numbered. It is the crustaceans who must change!

    Interesting question that occurs to me - what are the segments called in xiphosurans? I think they use the arachnid terminology, but I could be wrong.

  8. i literally felt something crawling on my neck while looking at that picture and punched myself in the throat in a panic....

    those critters are interesting though for sure.

  9. Since insects and crustaceans are sister taxa

    CMIIW, but I was under the impression that insects might actually be crustaceans (cladistically speaking).

  10. CMIIW, but I was under the impression that insects might actually be crustaceans (cladistically speaking).

    Might be. Or at least, Crustacea might not have any provable apomorphies relative to Insecta. At present, though, we have little idea whether or not Crustacea is monophyletic or paraphyletic in respect to Insecta, and if paraphyletic, which crustacean group(s) are Insecta/Hexapoda's actual sister (Malacostraca is a contender). Many people currently treat Crustacea and Hexapoda as sister taxa as a matter of convenience until things are better resolved.


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