Wednesday, October 31, 2012

Home Sweet Crypt

( Fair warning! Creepy-crawly Halloween issue! )

It was a warm summer afternoon when my brilliant friend, Bob, accidentally buried himself about eight feet deep, pinned beneath a plastic 1,000 gallon water tank that he was installing. Alone. Fortunately, the tank was empty and Bob slowly dug his way to the surface, living another day to tackle yet another home improvement project. As humans go, Bob is one of the most unusual specimens I've ever known.

As bugs go, one of the most unusual specimens I've ever met is a handsome, black and orange insect known as the "Sexton beetle" (Nicrophorus vespilloides, in my encounter).

Adult Sexton beetle (Nicrophorus vespilloides)
Adult Sexton beetle (Nicrophorus vespilloides)
Among us humans, the "Sexton" was the church employee whose duties included grave digging. The Sexton beetles were so named for their habit of burying their young with a small, dead animal. But this odd behavior begins to look pretty smart when you start digging up some of their other habits.

Like some of those southern tent-revival preachers, Sexton beetles can seem caring and creepy at the same time. They bury the dead with utmost care and cleanliness. They also provide bi-parental care (male and female) to their young - an extremely rare behavior in the insect world - while condoning cannibalism to keep their family size manageable. And to top it off, these beetles fly around at night with large, red mites clinging to them, which they shuttle from carcass to carcass like crowded, red-eye commuter flights.

These are large, handsome beetles, but they're mostly nocturnal and seldom seen (which also sorta' describes Bob). The Sextons make a living by taking care of small deceased animals, like birds and squirrels. Their antennae tips are enlarged and flattened to help them follow the irresistible aroma of cold cadaver (actually, three different sulphur-based compounds) wafting on a warm summer breeze.

The first male beetle to arrive at a fresh carcass defends it from other males while waiting for a female to arrive. If she's late, he assumes a stiff-legged posture on top of the deceased and releases a he-beetle pheromone to help bring her home. Sometimes, a male Sexton assumes this posture without actually finding a body, and proceeds to mate with any female Sexton who lands to inspect his larder. But only the last mating prior to egg-laying will beget her offspring.

Multiple Sexton beetles might cohabitate on a large carcass, but normally there is just one parental pair per modest cadaver. Both male and female excavate a grave beneath the body, or drag the departed off to softer ground if necessary. They remove feathers from birds and hair from mammals, roll the deceased into a ball, and carefully cover the naked body with special anti-fungal oral and anal secretions to slow down decomposition.

While helping her mate cover their new pantry with dirt and leaf litter, the female Sexton takes a break to lay her eggs in the soil immediately above the carcass. Both parents guard the crypt, and they make a small depression in the top where their grub-like larvae will gather after hatching, a day or two later.

Among larger Sexton beetle species, the young are completely dependent on parental feedings. The smaller species often feed their young, but their grubs can also fend for themselves. In general, adult males tend to guard more while females tend to feed the young more, but if one adult dies the surviving adult will successfully perform both duties.

Both parents feed their begging larvae chewed-up and regurgitate meat, while also working to keep the competing flies and maggots at bay. If too many fly maggots emerge, and the amount of food available becomes insufficient to provide for the whole Sexton family, the beetle parents will consume some of their own larvae ("filial cannibalism") to ensure that their remaining offspring grow up strong.

Mite hitch-hikers on a Sexton beetle
Mite hitch-hikers on a Sexton beetle
Sexton beetle parents also deploy a red army that helps them deal with the nefarious flies. Fly maggots are a favorite menu item for those hitch-hiking mites that cling to the adult Sexton beetles.

Upon arrival at a new carcass, the adult mites will disembark, partake of the bounty, flirt, mate, and eventually lay their own eggs alongside the Sexton's eggs. After the mite eggs hatch, this new generation of mite larvae quickly grow into non-feeding "deutonymphs," and it's these teenagers that hitch a ride to the next cemetery. Most of the early mites will gravitate to the adult male Sexton beetle, who departs from the crypt several days before his mate. Late-developing mites who miss both flights (about 14% of them) must wait for the young Sexton larvae to pupate and depart - which puts the late-blooming mites at a career disadvantage. 

About a week after hatching, the well-fed beetle larvae wanders off on a warm afternoon and buries himself in the surrounding soil to pupate. About two weeks later (or the following spring, for some Sexton species) a new adult beetle slowly digs his way to the surface, collects a few hitch-hikers, and flies off to sniff out a new home improvement project.

(Behind the beetle: I felt disappointed that I didn't get to count the mites on this fellow before he flew away. He was probably toting 8-10 mites, but I've seen photos of Sexton beetles covered with a dozen or more mites - now there's a Halloween costume idea!)