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)

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

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!)

Odonata Freeloaders

Red aquatic mites on the thorax of a dragonfly.

As summer winds down, we're seeing more and more adult dragonflies (order Odonata). And a good number of them are carrying various numbers of freeloading hitchhikers - aquatic mites. The parasitic mites will drop off when the dragonfly lays its eggs in water.

Round, red mites on the thorax (many) and abdomen (two) of a different dragonfly.

Mighty Mites

[ Fair warning -- if thinking about creepy crawlies makes your skin itch, you might just want to scroll on down and read the next post instead. ]

Mating dragonflies

Ah, the delicate and lovely dragonfly. A reminder of summer days spent playing in the water. Here, the red male dragonfly clasps the yellow female by the back of her head, and she reaches forward to collect a spermatophore from his mid-abdomen storage compartment -- the dragonfly version of sex.

But what's this, all these little golden guys clinging to the female dragonflys' abdomen? Could they be? Are they? Parasites? As one invertebrate biologist described it, these guys are like tiny versions of bloated ticks on a dog.

Welcome to the wonderful world of mites.

You already know some mite species by their common names. Chiggers, mange and scabies mites. Rust mites, dust mites and -- maybe the creepiest -- eyelash mites (more juicy details on them later).

Most mites look like tiny versions of spiders or ticks, their close relatives. Their fossil history goes back almost 400 million years, making them one of the earliest animal groups to crawl out of the ancient seas. Currently, the 50,000 species that have been described represent only about 5% of the estimated total. Mites are the most common animals in nearly every kind of habitat, but they are rarely seen because they are so darn small.

As arachnids, all mite species have a two-part, segmented body -- and that's about as definitive as it gets. They might have 1, 2, 3 or 4 pairs of hairy legs. The might have 1-5 eyes, though most are eyeless. Some species live in fresh water, some live in salt water, and others are terrestrial. Most are external parasites, but other species or age groups may be predators, vegetarians, or detritivores. Their life cycle typically follows as: egg, pre-larval stage, larval stage, then a series of 1-3 nymph stages.

On our delicate dragonfly, the mites are in their parasitic larval stage. They are living off the dragonfly's internal juices, but they probably won't adversely affect their lovely host. When this female dragonfly returns to the lake to deposit her eggs, the larval mites will drop off into the water. After a series of nymph stages, adult female mites will lay 20-400 fertilized, red eggs in the mud, under a rock, or attached to submerged vegetation.



Red mites (genus Arrenurus) on a blue damselfly

When a red egg hatches, a pre-larval mite will wiggle about in the water until it finds a suitable host to grab hold of -- like a dragonfly nymph. When the larval dragonfly climbs out of the water, splits its exoskeleton, and spreads its new wings to dry in glory, the tiny parasitic hitchhikers crawl aboard. In some areas, water mites parasitize 20-50% of the aquatic insect population.

After finding a new host (or meal), two segmented appendages ("pedepalps") grab hold from the mite's head end. Then the mite stabs with two retractable, snake fang-like mouth parts ("chelicerae"). Through these holes, digestive enzymes are injected into the host (or prey) item. The mite hangs on, sucks up the juices, and bloats up like a tiny tick. Mmmmmm.

Various mite species have adapted to thrive in hot thermal vents, deep sea trenches, and arctic extremes. And closer to home, there are 65 microscopic mite species that have specialized to live in the hair follicles of mammals -- including two species that live in grandpa's eyelashes.

Demodex folliculorum (first described in 1842) lives in hair follicles, while Demodex brevis lives in the sebaceous oil glands that are connected to the hair follicles. Both species are found primarily on the face, especially around the nose, eyelashes and eyebrows. These semi-transparent mites eat dead skin cells and extruded oils. And while they don't defecate on the skin (or even at all), they do crawl out at night to mate. In each follicle colony of about 10 mites, adults frolic at the follicle opening and then the females lay about 25 eggs inside. The eggs hatch in 3-4 days, then 7 more days to reach adulthood, with a total lifespan of 14-18 days.

Hosting these mites is quite common and usually there are no symptoms. Eyelash mites live in about 1/3 of all children, 1/2 of adults and 2/3's of the elderly. (Our skin might produce more cebum, or oil, as we get older.) You can even look for these mites by plucking an eyelash and examining it under a microscope.

Or, if that idea makes your skin itch, you can also look for mites in lots of other places.

Engorged mite hitchhikers

Though small, mites are very common. One square meter of the muddy debris at the bottom of a lake or pond may contain over 2,000 mites, while the same amount of cobble substrate from a mountain stream may contain 5,000 mites. A square meter of forest soil might hold a whopping 1,000,000 mites of 200+ species. And yet, how many times have you seen a mite in a lake, stream or forest? They may be everywhere, but they are mighty small indeed.

In fact, the name "mite" originates from the 12th century Dutch word for a small, golden coin. The huge family of tiny mites is very adaptive, and adaptability is the golden coin of evolution -- even the evolution of creepy crawlies.

Behind the lens: Following active insects from perch to perch renders most tripods and macros useless. I photographed these dragonflies with a short extension tube on a 70-200mm lens, hand held. This gave me a flexible close-focus zoom that still kept me 1-2' away from these shy suitors. Also, by removing the lens hood, I still had the option to use the on-camera flash for fill. 

Behind the bugs: Thanks to Bryce and "invertebrate guru" Dave, at the Montana Natural Heritage Program, for pointing me in the right direction to solve what had been a baffling mystery.