Monday, July 30, 2018
I had placed a white sheet and mercury vapor light near our creek and an old farrowing house. One night while checking the sheet I noticed an insect on the ground moving rapidly in circles on the ground in some soft loamy dirt. It was such odd, erratic behavior for an insect it caught my attention immediately. I watched it for some time before it occurred to me to catch it and try to identify it. It proved somewhat difficult to catch as it ran quickly under the dirt and scurried away. After several tries I was able to capture it and ID'd it as the Mosaic Round Sand Beetle. There are numerous beetles within this genus, with most of them located in the Northern Hemisphere. Examples of beetles within this genus may be found in North America, South America, Asia and Africa.
These strong burrowers are typically found in sandy areas near creeks, lakes and other water sources, which would explain its presence at the white sheet near the creek. A few species within this genus may be attracted to lights at night and apparently this is one of them. I would assume these are the industrious hunters as they feed on insects both in the adult stage as well as the larval stage. With all manner of insects being attracted by the mercury vapor light it was an all-you-can-eat-buffet for these night time hunters.
Their strong mandibles remind me of the jaws found on tiger beetles and look like they could cause some serious damage to unsuspecting insect prey. They have large bulbous eyes which I assume gives them good eyesight for spotting prey, and with the speed at which they move, catching a moving target wouldn't be too difficult.
It is assumed they spend the winter in the adult stage hiding among leaf litter as well as other protected areas. In the spring mating occurs, but I could find no information on where young are reared or how long it takes for them to complete their lifecycle.
At only 5-7 mm in length, they prove that sometimes the most interesting things come in small packages.
Sunday, July 15, 2018
In fact the name Nicrophorus is a variation of the word Necrophorus, and translates into "Carrier of the dead." Which is an apt description for beetles in this genus.
Hair or feathers are removed before the beetles coat the carcass in protective anal secretions they produce in order to discourage the growth of fungus. Once mated the female will lay eggs within the chamber. The adult pair will feed on the carcass and when the eggs hatch they will coax the tiny grubs to the carcass by using sounds made through stridulation (rubbing their legs together). Larvae are fed masticated bits of anal secretion coated carrion by the parents. Sounds like the stuff of a vomit inducing nightmare, but apparently if you are a carrion beetle this is pretty tasty. They are one of the few beetle genera in the World to exhibit parental care. Litter size is controlled by the parents as well; if they misjudged the size of the carcass and the food source runs low they will begin cannibalizing on the larvae to reduce their numbers so the food does not run out before the offspring can finish their development.
An accidental discovery made by a couple of researchers over a decade ago found these beetles utilizing another resource for rearing their young.....snake eggs. Most specifically black snake (Pantherophis obsoletus) eggs. These researchers were studying communal nesting sites of black snakes when they discovered many, if not most of the nesting sites overrun with pustulated carrion beetles rearing young on the eggs. They published their findings which was picked up on by some individuals who studied beetles within this genus. It helped solve a long held mystery of why this species was no longer found on mouse-sized carcasses in the wild, even though many other species within this genus are. This discovery has encouraged many researchers to study this phenomena within laboratory conditions. Published studies have found that N. pustulatus nearly always chooses snakes eggs over other proffered food sources, like mice carcasses. When offered both snake eggs and mice they will often drag the mouse carcass to the snake eggs, and utilize both food sources. Males produce larger levels of pheromones in response to snakes eggs versus mice or other carrion.
|Black rat snake eggs ready to hatch|
I would assume these beetles have found other such snake nesting sites on our farm and have used them for a food source. How the beetles locate the snakes eggs is still a mystery and up for much guessing and hypothesis. Do they follow the scent of damaged or decaying eggs? Do they follow the scent of the snakes themselves? Is it happenstance? Research may reveal the secret of how these beetles locate and utilize black snake eggs, but there is an equally good chance it may remain an unsolved mystery of nature.
|Newly emerged adult (L)|
These beetles reach lengths up to 20 mm (1 inch) and are black with bright orange or orange-red spots at the edge of the wings near the tip of the abdomen and a spot on either side of the wings. Like all carrion beetles they smell absolutely terrible when handled......after all a life among dead things is not exactly an advertisement for Chanel #5. It takes numerous hand washings to remove that odor, trust me!
|N. pustulatus with mites|
Carrion beetles, natures little decomposers, are one of the most important components to make up the natural world. They recycle carcasses, removing potentially diseased animals from the environment by feeding on them or using them as a food source for their offspring. This makes the environment healthier for other animals, including humans. The leftover bits and pieces of carrion that the beetles don't use provide beneficial nutrients for soil health. This helps plants thrive.
They may not be the most attractive of insects, and definitely do not hold the same appeal as butterflies, but they have a charm all their own and provide a much needed environmental service that should be respected and appreciated.