Insect of the week: 24 July 2023

Colletidae: Hylaeinae: Hylaeus sp.

This is Hylaeus species, a bee. Some years ago I would have thought otherwise. “Is it really a bee?” I’d have asked. It doesn’t look like a bee. Bees are densely hairy with branched setae giving them a bushy appearance. Does this thing even have hairs? Yes, it is a bee and yes again, it does have branched hairs on parts of its body, though you would need to look hard through a microscope to find them. In fact, ‘branched hairs’ is a synapomorphy, a character which defines the group of insects called bees and which, among invertebrates, is unique to them. The great majority of pollinating bee species possess an “organ” called a scopa, a dense, bushy assemblage of hairs on which copious amounts of pollen are stored after being collected. Depending on the bee family the scopa is found either on the hindlegs or on the underside of the abdomen of a pollinating bee. We already know that many bees do not collect pollen to feed their larvae but rather steal the food meant for the larvae of a pollinating bee species. These cleptoparasitic bees have far fewer hairs than do the hard-working host bees, and they lack a scopa – after all, why have a lot of hairs if you are not going to collect pollen from flowers?  What we have learned here is that there is more variability in the way bees look than we once thought. So, “is Hyaleus a cletoparasitoid?”, I’d have asked? Sorry, but no – Hylaeus is a genus of pollinating bees. Like cleptoparasitoids they lack a scopa and, for that matter, most of their hairs, but Hylaeus has developed a completely different method of collecting pollen. With their legs and their small mandibles they scrape pollen off a flower’s anthers and swallow it along with any nectar they have imbibed, storing the food in their crop, a part of their digestive system. Once finished they return to their nest to provision food among their larvae by regurgitating the pollen and nectar mix, in a manner similar to the way many bird species feed their young.

Hylaeus is a relatively successful genus with more than 500 species worldwide. Their common name is yellow-faced bees or masked bees. I prefer the latter name, and our insect of the week has a very nice mask. Hylaeus species are the only bees native to Hawaii, with about 60 species known from those mid-pacific islands. However, a recent census suggests that several of these species have become extinct, possibly a result of competition with adventive bee species. In the Afrotropical region Kenya has the largest number of Hylaeus species, 14. The specimen in the image was collected at Chorlim at the base of Mt Elgon.

Credits: Dr Robert Copeland