Essays

Wild On The Prairie: Invertebrates

Tick population explosion
July 28, 2002

"Our backyard is swarming with ticks! There is more ticks this year than ever before! What is going on?" I hear the same report and question every day, sometimes several times a day. "I pulled 22 ticks off of my dog. I let him out for a run after all the fussing, and when he came back in there were three more on him. Why is there such a population explosion?"

"Well, a female tick lays 3000 to 6000 eggs, but I would have figured the 11 degree freezes we had would have killed some of them, but I guess not! Another potential reason might be the drought. Coyotes have been spotted running down some alleys in some neighborhoods south of the loop. They and other wild animals have very little to eat out in the pastures, so the hungriest are becoming braver than normal. If one coyote had a half-dozen pregnant ticks that jumped off on one foray into town...you can do the math."

"How can you tell a female tick from a male?" The questioner is usually laguhing, expecting to hear that such an identification is impossible.

"By the folds of skin. Females need more blood for the production of eggs, so their body is designed to swell up to the size of a pea -- and they gain a hundred times their "empty" body weight. Males never swell up near as much. If you examine a tick under a microscope a female will have an alloscutum, while the male does not. In other words, the female looks like it has two seperate sections to its abdomen. And if you get really observant the female one fold behind its basis capituli, while the male has two. The basis capituli is the head part. "

"Like stretch marks!" one lady said. "Stretch marks before the swelling up -- I am glad we humans aren't that way."

When a tick has had its fill, it pulls its sucking mouthparts out of its host and falls to the ground. When the adult female has become engorged, she releases a pheromone, and a male tick on the same animal comes running. The adult female tick only stays on the host animal about 10 days, while males keep hanging on. She finds a place to hide and lays her eggs, which she transfers to her back. It takes a week or more, then she shrivels up and dies

When the babies hatch they hitch a ride on the first lizard, snake, mouse, porcupine or any other animal that spends much of its time on the ground. In the first instar, they have only six legs, but after they become engorged the first time, they fall off, molt and have eight legs. At this time they are the size of the period at the end of this sentence. Again they wait for another low-slung animal, and again engorge themselves. Again they fall off and molt, but this time some tick species use only one type of host mammal, while others take any sort of mammalian blood.

Even a just-born tick can wait up to a year for its first meal. One experimenter reported that a tick was still alive after four years without a meal. The first two instars wait on the ground, but the adult crawls up a grass stem and waits at or near the top.

A tick waiting for a host can not see it approach. They have no eyes. They wait, with their front legs raised, sometimes slowly waving them back and forth. Their organs of smell are located near the tips of the forelegs. The sensory apparatus identifies carbon dioxide, which helps them find resting animals (and lazy researchers using dry ice as bait!) If no dew is available if the tick becomes dehydrated, it falls to the ground and finds moist soil. This explains why ticks disappear in most west Texas pastures during the hot summer months, but not in well watered yards.

Ticks also are attracted to warmth, which they can sense for several centimeters. One research filled a bottle with different warm liquids, and if the forelegs were removed, the ticks would drink anything -- even acetic acid, salt water. Ticks must have no sense of taste.

The numbers of ticks on one animal can be astronomical. During World War II one training area became almost unusable due to ticks. One enlisted man had 294 ticks. A handful of animals were shot and 3064 ticks were found on a fox, 1,183 on a jackrabbit, 910 on one deer, 110 on another deer, and 1952 larval ticks on one bobwhite quail. In the shade of one tree 4086 adults were found in the leaf litter. Such high numbers of ticks can kill an animal. The animal steadily becomes weaker and less alert, resulting in it becoming easier prey.

American dog ticks and brown dog ticks are the most common species found in Midland County. Out in the pastures, rabbit ticks can also be found. Other species are also likely to be present, but I have not found any data collected by vets or health departments. Spray insect repellent on your shoes and pant legs when ticks are bad -- ticks can carry some unpleasant diseases!