Back burying beetle (Nicrophorus nigrita)
Spooky season may be over, but this week’s crawly deserves honorable mention as a gothic gravedigger. Meet the black burying beetle (Nicrophorus nigrita).
Here I do want to issue a content warning of sorts: I highly recommend you don’t sit down with a snack to read this. The black burying beetle is amazing, but their role in the ecosystem isn’t one you want to read about while munching on your popcorn.
That said, you really do want to meet these beetles. They’re fascinating and arguably the best beetle parents around.
Meeting a black burying beetle in real life is quite uncommon. There are only 51 recorded sightings of them in Oregon. Their secretive lifestyle factors into their hard-to-findness.
Black burying beetles are strictly nocturnal, and being black, it’s quite difficult to spot one when they are out and active. During the day they hide under leaf litter or under a layer of soft soil.
When night arrives, black burying beetles rise up, take flight and begin the serious process of raising a family.
The first thing a black burying beetle couple needs is a nice small carcass. The ideal carcass weight is 3.5 – 7 ounces. The beetles need a small carcass because they need to carry it to an ideal spot before turning it into home-not-so-sweet-home.
The beetles work together to scootch under the carcass, then lift it up and carry it on their wee backs to a protected spot with soft soil.
Fun fact: The beetles can smell a carcass (via their antennae) from up to two miles away. They may travel up to 18 miles to find the perfect dead mouse, shrew or bird (also one that hasn’t been claimed by any number of other carrion cravers).
Once the burying beetle duo has the carcass in place, they – as you might guess by their name – bury it. Fully bury it. They’ll excavate under the carcass until it’s deep enough to totally cover with the displaced soil.
Next they remove all the fur (or feathers, but usually fur) and mold the carcass into a ball. They cover the ball with bodily secretions (glad you didn’t grab that popcorn, aren’t you) which slows the growth of mold and bacteria.
Seriously. How cool is that? Don’t have a fridge? Just spit on your leftovers and they won’t mold.
With “dinner” ready for the future kiddos, the female black burying beetle digs a small chamber in the soil by the carcass and lays her eggs.
Remember, I said black burying beetles are the best parents? We’re really getting to that now. They’ve already gone to Herculean efforts (Sisyphean?) to ready the dinner table, but they will do so much more to ensure their kiddos are successful.
First the number of eggs the female lays is proportionate to the size of the carcass the parents found. Teeny shrew? She’ll lay 12 eggs. Nice-sized mouse? She may lay up to 25 eggs.
With many arthropods, once the eggs are laid and the brood chamber is provisioned with a good meal, the parents skedaddle. Not so with burying beetles.
Both parents will hang out, until the eggs hatch after about six days. During that time they will eat any competition – such as fly larvae – that happens to find their buried, balled up mouse. They try to preserve the entire carcass for the kiddos.
Once the eggs hatch, the adult beetles will create a little “bowl” at the top of the ball-o-carcass. They’ll regurgitate some nice partially digested dead mouse into the bowl for the kiddos and lead the larvae to the table.
Both parents will also directly feed their young their pre-chewed meals. Larvae will beg for food like baby birds.
Generally mom and dad beetle will stay with the young, feeding and protecting them until they are at their final growth stage and ready to morph into adults. Sometimes the males will leave a few days before that.
The new generation will morph into adult form in late fall, just in time to hunker down under leaf litter or in some soil to hibernate over winter.
Some adults will hibernate as well, but most live only one year so will die when the first freeze sets in, their elaborate and successful parenting job done.