There is a term that bird-spotters use to describe the ability to recognise what species a bird belongs to even if one cannot see the details of its features - they refer to the "jizz" of a bird, derived from the acronym GIS for "general impression and shape". The jizz of a bird species is not something that can be described easily, if at all - it is something that can really only be appreciated with experience. It should hardly come as a surprise that the same concept applies with identifying other organisms just as much as birds. Lacewings (Neuroptera) are a smallish order of insects (only about 5000 species) that include a diversity of forms, but many look at first glance not unlike small dragonflies. Still, a closer look will reveal significant differences to a dragonfly. For a start, lacewings have longer antennae and are able to fold their wings back over their abdomen in a way that no dragonfly can. There is also the feature that gives them their name - the wings of lacewings are particularly densely covered with veins, the little criss-crossing fluid-carrying lines that you can see on any insect wing. While you might need to look very closely indeed to see the individual veins, the cumulative effect of the dense veins is to give lacewing wings a distinctive shimmer, like light off satin, or the glimmer of colour across oil. This week's highlight taxon is a specific group of lacewings - the tribe Belonopterygini.
Lacewings have a complete metamorphosis, meaning they have a distinct larval stage separated by a dormant pupal stage from a very different-looking adult. Most lacewings start out life as formidable predators, and are quite recognisable by their large, protruding jaws. The most famous are the antlions of the family Myrmeleontidae, which dig themselves conical pits at the bottom of which they lie dug into the soil, waiting for any small insects unlucky enough to fall into the pit. While the large jaws are used for capturing and macerating prey, lacewing larvae are actually liquid feeders, injecting digestive saliva into their prey then sucking out the dissolved juices (Canard, 2007). One intriguing (yet kind of disgusting) feature of the order is that the midgut is not actually connected to the hindgut until pupation, meaning that the larva is not capable of defecation. Any indigestible waste products are stored in the gut until the lacewing reaches adulthood and passed after emerging from the pupa. Can you imagine the relief?
Belonopterygini are a cosmopolitan tribe of a different family, the Chrysopidae (green lacewings), whose larvae are active hunters, many of them of economic significance as predators of plant pests such as aphids and thrips. Belonopterygin larvae are specialist associates of ant nests (Freitas & Penny, 2001), feeding on the ants therein. Unfortunately, such specialist habits make Belonopterygini one of the less-studied chrysopid groups, and I have been unable to find how the larvae evade detection by the ants. Like other chrysopids, belonopterygin larvae use small bits of soil and debris to disguise themselves, starting with the shell of the egg they hatched from (Catanach, 2007). Larvae of other chrysopids have been observed to incorporate the husks of drained prey into their trashy disguises so I would be interested to know if belonopterygins do the same, as has been described recently for assassin bugs.
Adult chrysopids may be predacious like the larvae, or they may feed on non-live food such as honeydew. Honeydew-feeding species possess diverticula in the gut that house symbiotic yeasts aiding the lacewing in digestion. Sounds produced by tapping the abdomen on the substrate are used by chrysopids in courtship, and the pattern of sounds produced may differ significantly between closely related species (New, 1991). Eggs are laid perched on the end of long silk threads.
Canard, M. 2007. Natural food and feeding habits of lacewings. In Lacewings in the Crop Environment (P. McEwen, T. R. New & A. Whittington, eds.) pp. 116-129. Cambridge University Press.
Catanach, T. A. 2007. Abachrysa eureka (Banks) (Neuroptera: Chrysopidae): egg, first instar larva and biological notes. Unpublished thesis, Texas A & M University.
Freitas, S. de, & N. D. Penny. 2001. The green lacewings (Neuroptera: Chrysopidae) of Brazilian agro-ecosystems. Proceedings of the California Academy of Sciences 52: 245-395.
New, T. R. 1991. Neuroptera. In The Insects of Australia (CSIRO, ed.) pp. 525-542. Melbourne University Press.