Region III Quarterly

Volume 3 - No. 2

April, 1941


By Harold J. Brodrick,
Assistant Chief Ranger,
Carlsbad Caverns National Park.

"Poisonous insects" is not quite a correct title for this article as most of the species discussed are in the class Arachnida: scorpiOns, spiders, etc.; while the centipede and millipede are in the class Myriapoda. None of them is in the class Insecta or true insects. However, they are all called insects by the average person. People vary in their susceptibility or resistance to the poison involved in the bites of many of the insects; a bite unnoticed by one person may cause considerable pain and distress to another. Taken on an average, the black widow spider is the only one we have in the southwest that can rightfully be called dangerous.

Best known in the arid southwest is the big black tarantula. Formidable in appearance, and the subject of much fear and superstition, the tarantula merits the friendship of his human neighbors, for he feeds on grasshoppers and roaches. Equipped with sharp fangs, his bite is painful, but not poisonous to man. These spiders are not pugnacious and do nOt readily bite unless aggravated. Scientists know today that there is little justification for fear of our true tarantulas. One member of this group, however, a giant species of Central America, appears to be an exception in regard to its venomous nature.

Poisonous insects

Although science has exploded most of the exaggerated fears of spiders in general, it regards as dangerously venomous one small group found throughout most of the warmer countries of the world. The best known representative of the clan in the United States is the black widow, (Lactrodectus mactans) common in the south, but rare in the north. These spiders are rather closely related to the common house spider, but they have greatly enlarged poison sacs, and the venom is more potent than that of a rattlesnake. Black widows occur in nature under old logs and loose bark or other dark places near the ground. Near human habitations they are commonly found in stables, outhouses, and basements. The female is jet black, with a distinctive red hour glass mark on the underside. The black widows habitually hang upside down (see illustration) from their irregularly woven webs. The male is smaller and has several red and yellow streaks on the black background. He is not known to bite man. When food becomes scarce he is usually killed by his mate, hence the name, black widow. I have found many of the females, and some males, in the mud cases of the muddauber wasp, placed there as food for its larvae. Others were found nearby, in an apparently paralyzed condition, where they were dropped by the wasps.

The scorpion is another member of the Arachnid class, measuring from half an inch to eight inches in length. They live in tropical and subtropical regions, hiding in crevices, pits, sand, or under rocks during the daytime, but running about actively at night. They capture insects and spiders, tear them apart and devour the pieces. Larger animals are paralyzed by the sting on the end of the scorpion's tail. This sting does not serve as a weapon of defense unless the scorpion is hard pressed. The poison from the sting is deadly to small life. Some of the local people in some parts of Virginia call the harmless little bluetailed skink (a lizard), a scorpion, and think that it stings with its tail.

The Vinegarroon or Whip-scorpion is another Arachnid found in the warmer sections. Staying hidden by day under objects or in crevices, it comes out at night to capture its prey of spiders and insects, which it catches and holds in its powerful pedipalps, the pair of arm-like appendages terminated by a pincher-like hand similar to a crab's. It has acquired the name "vinegarroon" from the strong vinegar-like odor it occasionally emits when disturbed. This creature is ordinarily shy, is harmless, and makes every effort to get away when disturbed; however, when cornered, it frequently makes a show of fight, spreading its pedipalps menacingly. The pedipalps are armed with several sharp spines and are strong enough to puncture a person's skin. The lashlike tail appendage is not a sting.

The body of a big centipede is flattened dorso-ventrally and consists of from fifteen to over 150 segments, each of which bears one pair of legs, except the last two, and the one just back of the head. The latter bears a pair of poison claws with which insects, worms and other small animals are killed for food. The centipedes are swift-moving creatures. Many of them live under the bark of logs or under stones. The poisonous centipedes of tropical countries belong to a separate genus. They may reach a foot in length, and their bite is painful and even dangerous to man. The rest of the species are practically harmless. The small hook on the tip of each walking foot is for use in clinging to objects. Poison can only be transmitted by the pair of poison claws just back of the head.

The millipede is listed here only because many people mistake it for a centipede. It is harmless and does not bite. Its body is nearly round, while the centipede's is flat, and it has from about twenty-five to more than 100 segments. Almost every segment bears two pairs of appendages. The millipedes move slowly, in spite of their numerous legs. They live in dark, moist places, and feed principally on vegetable substances.

Several of the true insects, such as bees, wasps, and hornets, are really poisonous, but ordinarily in a mild way. However, their stings might produce worse effects on some persons than would the bite of certain Arachnids.

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Date: 17-Nov-2005