Blister beetle love
Location: Westport, Ontario
October 7, 2010 10:00 pm
My wife and I came across these blister beetles getting some action at our cottage near Westport, Ontario, just north of Kingston. I guess the larger is the female, and she will likely store the sperm until spring, at which point she will allow fertilization to occur and get to the business of laying eggs. Any thoughts on if that is close? And any chance that you recognize the species? Thanks,
Signature: Ian in Ottawa
Your Blister Beetles are Oil Beetles in the genus Meloe, also known as Oil Beetles. BugGuide indicates that there are 22 species in the genus, but there is no explanation on how to identify them or how to distinguish them from one another. With that said, we do not feel qualified to identify this amorous pair to the species level, but we will not give up on getting an answer for you. At the end of the “browse” section on BugGuide, which can be used to further narrow the identification on an insect by moving more thoroughly through the taxonomy, often to the subspecies level, is a page that is called “images seen and deemed unIDable by Dr. Pinto“. This piqued our curiosity, and we decided to try to find out more about this expert in the genus Meloe. Our search toward the identity of Dr Pinto led us the first page of an online journal article entitled The Sexual Behavior of Meloe (Meloe) strigulosus Mannerheim written by John D. Pinto of the University of California, Riverside. On the UC Riverside website, we learned that Dr. Pinto is a Professor of Entomology, Emeritus, and there is a contact email address for him, so we will attempt to get an answer from him regarding the species of your Oil Beetles.
The life cycle of Blister Beetles is very interesting and complicated in that the larva undergo morphological transformations that are more complex than other beetles. There is a mobile larval stage known as the triungulin, and later instars are more sedentary. The Featured Creatures section of the University of Florida Entomology Department has an excellent page on the life cycle of Blister Beetles. The larvae of the Blister Beetles in the genus Meloe live in the underground nests of solitary bees, and BugGuide has a detailed explanation of the life cycle of the larvae, including this information:
“In at least one Meloe species, the larvae climb to the top of a grass or weed stalk as a group, clump together in the shape of a female solitary ground bee, exude a scent that is the same as, or closely resembles, the pheromones of the female bee, and wait for a male ground bee to come along. When he does, he tries to mate with the clump of larvae, whereupon they individually clamp onto his hairs. He then flies away, finds and mates with one or several real female bees, and the larvae transfer to the female(s).
Each impregnated female bee then flies off and builds one to several nests in burrows she digs in the soil, and the larvae transfer again to the new nests. The female bee stocks these nests with honey and pollen for her own young, but the hungry blister beetle young are there to gobble up the provisions. They eventually pupate and finally emerge as adult flightless beetles. Brothers and sisters find each other and mate, produce eggs and the hatchlings start the process all over.
Then there are male beetles from a couple other beetle families who seek out blister beetles, climb onto them and lick off the cantharidin the blister beetles exude. Not only have these other beetles developed a resistance to the cantharidin, they use the blistering agent to impress a female of their own species who then mates with them, whereupon most of the cantharidin is transfered to the female in the form of a sperm packet. The eggs the female subsequently lays are coated with cantharidin to protect them from being eaten before they hatch.“
Alas, we cannot with any certainty respond to your question regarding the storing of the sperm by the female, but most solitary bees are active in the spring and not in the autumn, so your guess seems sound. Perhaps Dr. Pinto can provide additional information should he respond to us.
Ed. Note: Here is our email to Dr. Pinto
Dear Dr. Pinto,
My name is Daniel Marlos and I have no entomology background, nor any scientific credentials for that matter, but that has not stopped me from maintaining the What’s That Bug? website since 2002. Through my pop culture website, I hope to encourage the web browsing public to appreciate the wonder of the lower beasts and to help them understand the important place insects and other bugs occupy in the complex ecosystems of our fragile planet. Someone sent in photos from Ontario yesterday of mating Meloe species and would like them identified and I found you by searching BugGuide and then following some search threads to your profile on UC Riverside. If you could identify the species in these photos, it would be awesome, but even more, if you could provide any information on this question posed by the person in Canada who took the photos: ” I guess the larger is the female, and she will likely store the sperm until spring, at which point she will allow fertilization to occur and get to the business of laying eggs. Any thoughts on if that is close?” I have been unable to locate any information on whether the female hibernates or if she lays eggs that overwinter. Any assistance would be greatly appreciated.
Dr. Pinto Responds
The Meloe photo is of Meloe impressus Kirby, a relatively common species in autumn in certain parts of North America. Females of this species lay their eggs relatively soon after mating, and the eggs overwinter and hatch the following spring. Actually it is more accurate to say that the first instar larva develops rather quickly but doesn’t break out of the egg until spring – at least that is what happens in the lab. Minor point but I might add that it is not entirely clear if the beetles in the photo had mated or not. After successful mating the pair lines up in an end-to-end position for one or two hours. The male in your photo was either still courting or in the first stage of mating before assuming a linear position. Much of what is known about North American Meloe can be found in — Pinto, J. D. & R. B. Selander. 1970. The bionomics of blister beetles of the genus Meloe and a classification of the New World species. Illinois Biological Monographs, #42. Only 1 new species has been described since 1970.
Sincerely, John Pinto