Since it's still cold outside, and there's no beekeeping to do, I thought I'd take a look at some of the particularities of the honey bee's life. One of these is the sting. As I mentioned in a previous post, the sting of a honey bee is a modified ovipositor - which is why only female bees can sting.
It's worth looking at a bit of taxonomy, because it helps to understand how bees and wasps are related, and why they both have stings. Bees and wasps are both members of the order Hymenoptera (bees, wasps, hornets, ants, sawflies), and all Hymenoptera females have an ovipositor, and so therefore do all female bees and wasps.
Within the Hymenoptera is the infraorder Aculeata, which contains bees, ants, hornets and some wasps (but no sawflies).
Outside of Aculeata, all other members of Hymenoptera (such as the sawflies, chalcid wasps and ichneumons) are unable to sting. But Aculeata is really interesting in the evolutionary history of Hymenoptera because the Aculeata are the only members of the order that can sting.
Actually, there are plenty of members of Aculeata that can't sting - either because their ovipositor is modified differently, or because they've lost the sting - both of which have happened over the course of evolutionary history. But we do know that the Aculeata all descended from one common ancestor species that lived sometime between 224 and 190 million years ago around either the end of the Triassic period or the beginning of the Jurassic. And that species had a sting.
We also know that the bee lineage (the clade Anthophila) separated from the ancestor of common wasps and hornets (the subfamily Vespinae) around 130 million years ago. An interesting thing happens after the lineages separate - the chemistry of the venom changes with evolution. In the bee lineage, stings are acidic, whereas wasp stings are
Back to taxonomy; following the family tree down further, we get to the family Apidae and sub-family Apinae. And finally we arrive at the genus Apis, which is the collection of 7 species that are referred to as honey bees. My bees are the species Apis mellifera, but this is not the only species that are kept by beekeepers - in Asia, beekeepers keep colonies of Apis cerana. On the other hand, Apis florea and Apis dorsata are not kept species - though people do harvest the wax and honey from wild colonies.
If we look back to evolution we find that the common ancestor of the Apis genus lived around 55 million years ago. And that common ancestor probably had a barbed sting, which is a feature common to honey bees. Other Hymenoptera didn't get this mutation, which is why honey bees are the only Hymenoptera that have a barbed sting - so they're the only ones that die when they sting you.
The actual structure of the sting is interesting. The bit that penetrates the skin is, in simple terms, composed of three structures. There is a pointed structure called the stylet, and two barbed structures called the lancets. These are arranged roughly in a triangle, with a central canal running down the middle of the triangle. The venom is delivered through the canal.
 |
| Diagram of a honey bee sting |
At the internal end of the stylet is a bulb, which is the venom gland. And at the internal end of the two lancets are two pairs of muscles. When the bee stings, these muscles cause the lancets to slide up and down along the shaft of the stylet. This is the clever bit - when one lancet moves up, the other moves down, and vice-versa. And because of the barbs, which grip on the up-stroke but not the down-stroke, it has the effect of pulling the sting further down and deeper into the skin of the victim. Even more clever - after the bee flies off, tearing the sting away from her body and leaving it embedded in the victim, the muscles keep working, the sting continues to dig into the victim's skin and the venom keeps pumping out of the bulb and into the victim.
So next time you're stung by a bee, just remember that you have had personal contact with a really amazing piece of evolution.
Further Reading
If you like reading science (and who doesn't?!) then this link is a fascinating analysis of the evolutionary history of Hymenoptera. And if you'd rather just look at pictures, then the cladogram (family tree) on page 1015 is a joy:https://www.cell.com/current-biology/pdf/S0960-9822(17)30059-3.pdf
This is a much more comprehensive description (with diagrams!) of the structure of the bee sting:
http://www.dave-cushman.net/bee/stingstructure.html
No comments:
Post a Comment