Wednesday, October 19, 2011

Burying Beetles

There exists an interesting, if relatively unknown, group of beetles that are common in the environment and very rarely seen that serve a much-needed function and go about it in a cool way.

Nicrophorus orbicollis, Wrentham, Sept 2011
These beetles members of the carrion beetle family (Sirphidae) and are unique in that they bury the carcass of whatever animal they plan to use and lay their eggs in it. The parents work together to dig out all the dirt from underneath a dead animal, say a mouse or a small bird, and then prepare the carcass by removing all feathers or hair and covering it in oral and anal secretions that keep the carcass fresh for longer (see: http://www.bbc.co.uk/news/science-environment-14669012). Both parents then care for the larvae for a couple weeks until they grow enough to pupate. Because of this "gravedigging" behavior the genus, Nicrophorus, is also known as the sexton beetles, as a sexton is a somewhat antiquated term for gravedigger.

N. americanus larva, July 2011, Nantucket
We have a bunch of species of Nicrophorus in the northeast and unless you really go looking, they can be difficult to find. The easiest - while a bit gross - way to search is to by setting baited (rotten meat) pitfall traps and checking them daily for beetles. Before I delve into an interesting story, here is a pictorial guide to the species you might encounter.
N. orbicollis, notice the black pronotum (section behind the head) and the small amount of orange on the elytra (wing covers) - this is probably the most common species encountered in the northeast.
N. marginatus, notice the orange on the elytra is extensive and connects the two crosslines (maculations) on the side. A common and sometimes quite large species.
N. sayi, a fall-flying species that has the front maculation (remember that vocab) extending forwards with an orange stripe on the side. Uncommon. Wrentham, Sept. 2011
N. tomentosus, a common, day-flying, small species that is easily distinguished by the yellow hairs on its pronotum.
Before we get on to the last two species (the two least common), it should be pointed out that the tomentosus above has a cool trick up its sleeve. The underside of the elytra is bright yellow, as is the upperside of the abdomen and it simply throws its wings and middle legs up and buzzes around during the day, looking convincingly like a bumblebee - an animal that many predators avoid!

Not a great picture, but it looks rather bumblebee-like, doesn't it?

The next beetle I have never encountered, but trapping in New Hampshire, my good friend and fellow bug nut (direct to him all mite questions), Will Cioffi caught this species, N. defodiens.

Notice the all black antennae on. It is a northern species, I don't know whether it reaches MA. Photo thanks to Will Cioffi.
And the last species demands a full story and many pictures as it is the one "famous" beetle of the genus: the American burying beetle, N. americanus. The largest species in the genus, reaching almost 2" and 3 grams at times, the American burying beetle historically ranged throughout the entire eastern United States in every state from Maine to Florida and out to Texas and Nebraska in the west. However, the beetle has all but become extinct in the last 100 years and is now one of the only beetles (one of the only non-butterfly insects) on the endangered species list. A natural population persists on Block Island, RI and another in small parts of Texas/Oklahoma/Nebraska.

N. americanus, notice the orange pronotum. This is a male, indicated by the orange square above the mandibles.
Because of its rarity and the success Lou Perrotti at the Roger Williams Park Zoo and others elsewhere have had in breeding the species in captivity, several reintroduction efforts are now underway - though we still do not know exactly what pushed this species off.

Was it widespread pesticides? The loss of the Passenger Pigeon and Heath Hen as suitable food? Can they not deal with development? Interestingly, a new paper shows that Opossums eat these guys preferentially over carrion and they are a species that has exploded and massively expanded their range in the past 100 years - and there are no opposums on Block Island and coyotes keep them in check out west. Unfortunately, all of these post-hoc hypotheses are just that, and we will never know for sure the reason for the decline.

#40 blue, a female (orange triangle above the mandibles), part of the reintroduced Nantucket population.
I got to work on this reintroduction effort this past summer on Nantucket with the Maria Mitchell Association and Roger Williams Park Zoo and I really felt it as a worthwhile and hopefully successful venture. While the government is spending millions of dollars on reintroducing Black-footed Ferrets, California Condors and Aplomado Falcons - this project probably costs less than $10,000 a year and has shown some preliminary success. The population grew steadily from the first introduction in 1994 until this past year when help - in the form of carrion - was cut off from the population in order to figure out whether the beetles could reproduce on their own. We found a low level of natural reproduction occurring, a very good sign. Overall, there are many interesting insect reintroduction and conservation projects occurring that simply do not get the press that the big animals do. There is a cool one occurring now to reintroduce an extremely rare (but once abundant) tiger beetle to Monomoy NWR on the Cape, though it is still only a few years in - I will be following it closely.

6 comments:

  1. just seen one of these in our backyard. we are in northwestern ontario. It had a bunch of small white bugs on her belly. Not sure if it was her babies.

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  2. entirely different species out there, I presume. The white creatures on the belly are actually Phorid mites, which the beetles truck around from carcass to carcass, allowing them to feed on fly eggs - which compete with the beetle larvae for carrion. Quite a cool mutualism and very commonly you see beetles FULL of these mites. In the first picture you can see a mite or two on the pronotum.

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  3. I hang fly traps in my Dog Yard and went out the other morning to change it and it was FULL of these. Which has never happened before, usually it is only fly when I change it. I was a little startled :)

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  4. wow - interesting, where are you? did you save any of them?

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  6. My insect obsessed two-year-old daughter just found N.tomentosus in our backyard. I've never seen one before and am extremely proud of her keen eye! Your blog helped us identify it. I would attach the photo of her holding the beetle, but appears I can't. Thanks for the great post!

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