BY ALPER ÖZKAN (MSN/PhDIII)
d_ozkan@ug.bilkent.edu.tr
In honor of the recent feast day of St. Valentine, patron saint of beekeepers and bubonic plague (among other, less important things), this column will be devoted to bees and their extended family—that is to say, wasps, ants and sawflies (but not termites, as these are social cockroaches), which together comprise the third-largest insect order, Hymenoptera (beetles, for the record, are the first, and are followed by moths and butterflies, though they may be overtaken as more species of diminutive parasitic wasps are described). Since there is a lot to say about this incredibly diverse and species-rich taxon (there are some 150,000 described hymenopteran species, and that is some 25 times the number of known mammals, which I must stress are a class instead of an order—come to think of it, a “standard mammal unit” would seem to be a nice way to describe the sheer diversity of groups with far too many species, with the beetle order clocking in at over 70 mammal units, while butterflies and moths are around 30, flies around 20, the orchid family about 4 and true grasses a bit below 2), I will only highlight a couple of favorites in each major grouping, starting from the most basal and moving on to the more derived.
Sawflies are the most basal hymenopterans, and distinguish themselves by lacking the narrow waist found in wasps, ants and bees, which makes them look less like wasps and more like flies. Their larvae, too, are uncharacteristically independent—while bee and wasp grubs are completely reliant on the provisions of their parents, the caterpillar-like young of sawflies forage for themselves, and may unite into swarms that both protect the individually feeble insects and allow them to devour their way through foliage by the combined force of several dozen mouthparts. While the adults are armed with a wicked-looking ovipositor, sawflies are altogether harmless to humans (the ovipositor is used to cut plant tissues, into which the eggs are laid), though the larvae of the Australian species Perga affinis are known to extract eucalyptus oil from their host plant and spit this at potential offenders, which should cause quite a bit of pain if a lucky larva manages to nail the eyes of an onlooker (but since it merely blinds, instead of killing outright, this sawfly is among the least dangerous animals on the continent—unless the eucalyptus oil combusts, which it readily does, although probably not in mid-air).
Not all sawflies conform to this standard, however: some use their drill-like ovipositors to deposit their eggs in wood (and can be major pests), while others go a step further and employ the same mechanism to lay their eggs in insects that live in wood. The ancestor of all true wasps, as well as that of ants and bees, is thought to be a sawfly of this sort, and I suspect that its ability to parasitize other insects has led to a massive increase in diversity (parasites, by necessity, are often specialists in the extreme, and can diverge very rapidly once they start exploiting different groups of animals). Whatever the case may be, the point remains that the most distinguishing feature of the remainder of the Hymenoptera is parasitism: a great number of wasps begin their lives by tearing their way out of something that was once (or is still) alive. And they use ingenious strategies to do so: there are wasps that lobotomize cockroaches to drag them around at their leisure, wasps that drug caterpillars into acting as guard dogs for the very pupae that tore their way out of their bodies, wasps that alter the web-spinning behavior of spiders to construct silken rain shelters, wasps that secrete hormone analogues to stunt the growth of hosts and wasps that inject mutualist viruses to shut down host immune defenses. Not even the most vicious of predators are beyond their reach: spiders are the favored enemy of most parasitic wasps, and one particular species even attacks antlions, using its well-armored hind legs to lock the monstrous larva’s jaws before injecting its eggs into its throat. Non-parasitic species are equally competent hunters: their stings are often used to paralyze their quarry, which is carried back to the nest and provisioned to the developing larvae.
And within this motley crew has arisen one group that is distinguished by the modification of the ovipositor into a sting—called Aculeata, this group includes the familiar yellow jackets, honeybees and ants (bees and ants, therefore, are quite conclusively wasps, much in the same way that birds are dinosaurs). I believe they need no introduction, but it is notable that it was once thought that honeybees were created from animal carcasses, which actually produced swarms of bee-mimetic hoverflies—and while long debunked, the story did have a sliver of accidental truth in it, as there are bees that really are attracted to carcasses: three stingless species, collectively called vulture bees, collect rotting flesh instead of pollen and ferment this into a sort of corpse-honey, with which they feed their larvae. As for ants, their industriousness is likewise legendary, but I should note that there are “slave-making” ant species that are wholly incapable of caring for their own broods, or even feeding themselves (though there are intermediate forms that can switch between slaving and traditional brood care, as the situation demands). These slavers instead bring larvae and pupae of other species into their nests, where the emerging workers will be imprinted onto the alien colony and begin serving its needs instead of their own.
There are many other curious bees and ants—those that swim in pitcher plants and those that cover their nests with silk wallpaper, those that catapult themselves using hypertrophied jaws and those that drink the blood of their own offspring—but I suppose I’m running out of space. Into another column they will go.