Insect Picture of the Day

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Here is the same carrion beetle, Nicrophorus tomentosus, from yesterday, but this time on its back. YIKES! What are all those bugs?!?

They are not its young. Those are parasites.

That’s a pretty severe infestation, isn’t it? These mites are phoretic parasites, meaning they cause no harm to the beetle; they’ve just climbed aboard for a ride. But even still… I’ve seen bugs climb aboard other bugs before. Normally it’s like five or six mites on a beetle. How come so many mites climbed aboard that one beetle? And how come the beetle let them climb aboard without preening them off?

I told you this bug was so cool it needed two days on the site….

Okay, so let’s review: this is a beetle that cannot reproduce unless it finds the corpse of a small dead animal. How often do YOU find dead animals lying around? Furthermore, the beetle has to be the first on the scene at the corpse: other carrion eaters may be eating the corpse, and other insects may have already colonized the body. The newlywed beetles will bury the corpse to protect it from other predators. But what if another insect has already laid eggs on the body?

Like flies. Flies are much more mobile than carrion beetles, and they can smell the carrion too. Furthermore, it takes up to 24 hours for the beetles to get the corpse properly buried. The opportunity for a fly to lay eggs on the corpse are pretty good. Fly maggots can overrun a corpse and severely reduce the survivability of the carrion beetle’s brood. Things look pretty grim indeed for our friend the carrion beetle.

Guess what those mites like to eat?

Phoresy means using another animal for transportation in a way that doesn’t harm the host. But those mites aren’t just riding the bus. They’re riding the lunch bus. They eat the fly eggs and even newly hatched fly maggots, and leave the beetle eggs and larvae alone. Then they move on, looking for another passing beetle to take them to another carcass.

This has to be one of my all-time favorite pictures from this site now, because when I first flipped that beetle over I went “Uaaahhhhh! GROSS!”… and then when I found out what was going on, I cried, “HOW FREAKING COOL IS THAT?!?”

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Okay, this bug is so freaking cool that it gets a two-day run. Tomorrow we’ll flip it over and talk about its underside. This is a carrion beetle, Nicrophorus tomentosus. It’s about 20mm long, and it walked out of my lawn last Saturday. Special thanks are due to bugguide.net for ID’ing this one for me.

Carrion beetles need a tiny corpse, such as a dead mouse or vole, in order reproduce. When they find one, they use pheromones to attract a mate. After mating, the male and female stay together until their young are raised.

As with any healthy relationship, the first thing the young couple must do is hide the body. Over the next 24 hours, they bury the corpse and dig a crypt around it, stopping to mate, on average, about 70 times. (Ah, newlyweds!) Then the female lays eggs on the body. After that, she will spend most of her time tending the brood and the male will guard the crypt, though the parents will occasionally switch off to relieve the monotony. If one of the parents dies, the other one will assume both duties and the brood still stands a pretty good chance of survival.

I always find amazing things when I look at bugs. For example, when the female carrion beetle reaches maturity her ovaries develop and all the preparations for reproduction are made, but then the whole process just stops, almost like she has laid a foot on the pendulum of her biological clock. When a male attracts her, she checks out the male, inspects the corpse by patting it with her forelegs and antennae, and she even inspects the ground to see if it is suitable for digging. Then, and only then, does she choose to ovulate: her body floods with hormones and she and her mate get to work digging (with the aforementioned frequent pauses).

If more than one beetle finds a corpse, the males will fight amongst themselves, and the females will do likewise, until all but the strongest of each gender have been driven off, and the winners of each gender will mate. If the corpse is large, more than one female may colonize it; if it is particularly large more than one mating pair may colonize it. What fascinates me is what happens near moderately large corpses–large, but not quite large enough to support multiple broods. The male will continue signaling to attract females… at which point the female on the scene will physically interfere, by pushing him over, jumping on top of him, and pinching him with her jaws.

I think it’s kind of sweet. She’s ovulating for him, she’s going to dig a crypt with him, and she’s going to raise a brood with him for the next several weeks. I think she’s entitled to a little jealousy.