[Stinging Insects] Legs

I’ll bet the average human being reacts more strongly to a house centipede than any other living creature. It can’t just be me. There’s something downright freaky about all those long, hairlike legs sweeping along with such uncanny speed and agility, not to mention the darn thing also is venomous. What a pleasant surprise to find in the tub! The raw impact of meeting one is the subject of an impressive number of stories in the blogosphere, and it may be the only household pest to be celebrated by a song titled after its scientific name. Yes, indeed, indie rock fans, check out “Scutigera Coleoptrata” by the Watched Pots. Apparently the songwriter had one of those typical close encounters in his bathroom, with the centipede coming out second best. “It was your fault,” go the remorseful lyrics, “You came out of nowhere way too fast.”

In addition to its eye-catching presentation, there is much that is remarkable about this distinctive creature. It clearly is not your average centipede in many different ways.

THE CONFUSING CENTIPEDE. Although everybody knows what they look like, a quick tour of the literature tends to confuse, rather than illuminate, the house centipede’s scientific name, country of origin, and even their normal habitat. When I was a student, its formal designation was widely taught as Scutigera forceps — nowadays, as the last in a series of four name changes since it was first described by Linnaeus in 1758, the species has stabilized (at least for the time being, and often spelled wrong) as coleoptrata. Many references still assert that it was introduced, or migrated northwards, from Mexico. At this point, the experts feel it originated in southern Europe and, through travel and commerce, has spread worldwide as a stowaway. And, although its common name is accurate as far as it goes — it is indeed the only type of centipede that can live and reproduce entirely inside modern buildings — it is perfectly happy outdoors as well, and has been found under woodland leaf litter far from any structural habitat. Not surprisingly, it also has been recorded from caves.

LEGS AND EYES. Two aspects of its anatomy immediately separate Scutigera from all its other relatives. The most obvious are those spider-like legs, much longer in proportion to the body than in any other centipede group. Although the word “centipede” literally means “hundred-legger,” no species has exactly that number and most have far fewer. In fact, a newly hatched house centipede is a stubby little thing that zips around on only four pairs of legs. These gradually increase in number, as the body lengthens with successive molts, to 15 pairs in an adult. The legs are much longer toward the rear, giving Scutigera a stride that greatly exceeds the length of its body. And rather than being used for locomotion, its last pair of legs is modified into truly spectacular, whip-like appendages that are even longer than the antennae and probably serve a similar, sensory function. Let’s face it, this creature doesn’t really look like anything else on earth.

(Extra bonus fact: The largest number of legs on the planet is an astounding 750 on a tiny species of millipede from California that was just rediscovered in 2006 — 80 years after the last time it was collected!)

Also distinctive to the trained eye is Scutigera’s body, the top of which is fused into only seven plates. This means it has to stay pretty much in a straight line as it moves, rather than flexing at every segment with the sinuous, snakelike movement of typical centipedes. The laterally constrained anatomy is actually better adapted for sheer speed. Despite its relative fragility compared to other centipedes, S. coleoptrata has been clocked at the mindblowing rate of nearly 1½ feet per second, making it one of the fastest land arthropods in the world.

The second most distinctive aspect of house centipede anatomy is its eyes. In contrast to the simple ocelli — or no eyes whatsoever — of other centipedes that find prey essentially by touch, Scutigera eyes are large, compound structures that noticeably bulge toward the front. They are watchful, predatory eyes, well adapted to keying in on form and movement. Surprisingly, they function similar to the eyes of daytime foraging insects like honey bees, containing photoreceptors that are highly sensitive in the blue to ultraviolet range.

THE CLAWS THAT CATCH. Strictly speaking, centipedes do not bite — their jaws are fairly innocuous, obscured by other mouthparts and reserved for chewing. The toxic weaponry actually consists of two modified front legs, located behind the head, that are commonly called “poison claws.” However, since the substance they deliver is technically a venom (i.e., a toxin injected by a sharp body part) rather than a poison (i.e., a toxin that is harmful when ingested or absorbed through the skin), I never thought this term was particularly appropriate. Best to call these fang-like pincers by their proper name, which is “forcipules.” As with its other appendages, the forcipules of Scutigera are much longer and more slender than in other types of centipedes.

House centipede bites (oh, okay, it’s a convenient expression) are extremely rare, and the effects are normally like a bee sting — an “ouch,” followed by a vengeful annihilation of the centipede, followed by pain and swelling at the site of the bite. As would be expected from any sort of envenomation, now and again somebody has the bad luck to react more severely, although nothing truly serious has ever been recorded.

For the centipede’s prey, it’s a different story. Scutigera is a killer to be reckoned with, laying waste to virtually anything it can subdue. One author termed it “the ultimate house cleaner,” since it disposes of most other creepy crawlies that our clients despise. If presented with several small prey items at once, it turns out those long, skinny legs are prehensile — the house centipede can actually snare and hold as many as five victims at a time. It’s death on arachnids, and apparently regards a building infested with brown recluse spiders as nothing less than heaven. No wonder it’s been proposed — well, not by anybody with any credentials — as a biological control agent against this far more serious pest. And it eats bed bugs! What’s not to like? 

And yet all of these beneficial attributes notwithstanding, the typical homeowner who sees a house centipede on patrol will immediately want it dead, dead, dead. For those of you firmly entrenched in the 1950s, any appropriately labeled product with a residual effect will work on them, although you’d have to apply a boatload of the stuff to have any chance of intercepting them in all the places they could appear. For those of you on the cutting edge, a good IPM approach is to “sub out” the work to a frisky cat — he may not be able to catch the critters, but he’ll sure chase ‘em around a lot.

Other than that, properly deployed sticky traps will work wonders, as house centipedes tend to hug the baseboards as they travel on the floor. The traps should also clarify what the centipedes are feeding on, which obviously are part of the problem. Finally, as holds true for so much else, reducing moisture as much as possible, in as many places as possible, will keep their numbers down.

’PEDES AS PETS. Old-fashioned or new wave, for all you hardened pest control professionals who still can’t suppress an illogical shudder at the sight of a Scutigera, now would be the time to put things into perspective. Let’s talk about the centipedes that can make your blood run cold for perfectly logical reasons.

The operative word here is Scolopendra, a widespread genus throughout the tropics that includes some of the largest centipedes in the world. Reaching over a foot in length, these awesome hummers are venerated by a select fraternity of “pede” fanciers who are forever searching the back alleys of the exotic pet trade for new forms to rear and show off to their friends. It’s not a hobby for beginners. Giant centipedes are powerful, nervous, and can stick you with a whopping dose of venom in the blink of an eye. And since you can’t handle them, train them, or take them for walks, there is really only a single, basic payoff to owning one — that would be feeding time.

Most of us understand that the brutal eating habits of predatory animals are normal and necessary in the great scheme of things. But that doesn’t make it any easier to watch. There is an infamous home video of a captive giant centipede killing and eating a white laboratory mouse that was posted on the Web early last year, and promptly copied onto many other sites. I won’t go into the more graphic details here, but suffice to say it’s well over the top. Striking like a snake, impaling and totally overwhelming the mouse, the centipede grasps the lifeless body in its massive forcipules and first five pairs of legs, and effortlessly carries it around the container before settling down to feed. Within just a few minutes, the rodent is macerated into a shapeless mass.

When it first appeared, the lurid film provoked a firestorm of outraged criticism by folks who viewed it more as pornography than as biology. I believe it goes without saying their reaction would be rather different if it was the fuzzy mouse eating the invertebrate. Nevertheless, I’m thinking that since people in our line of work are used to relating to a much smaller world, a pet house centipede might be an excellent (i.e., safer) substitute for satisfying one’s morbid fascination with the attacks of a formidable, alien hunter. So keep an eye out. Bane of the bathtub, silent and remorseless, legs may be coming out of nowhere way too fast at this very moment.

The author gratefully acknowledges Dr. Nancy Breisch for having nerves of steel when it comes to working with even the most alarming arthropods, and Dr. Earlene Armstrong for graciously making her monster pet Scolopendra available to be photographed. The opinions expressed herein are the views of the author and do not necessarily reflect the official policy or position of the U.S. General Services Administration.

The author is regional entomologist for the U.S. General Services Administration in Washington, D.C.