Alice Beltran, age 12, of Casmalio, Calif., for her question:
Are leeches and ticks related to each other?
We ordinary folk tend to regard ticks and leeches as repulsive creatures. Usually one such repulsive story is enough to last us at least a week and here we are with two on the same day. It helps to know that biologists can observe such animals without horror. So let's take a deep breath and face the fact the even the ticks and leeches have a rightful role in the scheme of nature.
Whether we like it or not, we share our world with about 250 different leeches and 15,000 tick type creatures. All of the leeches and most of the ticks are bloodsuckers but the two groups are not related to each other.
Scientists classify the million or more members of the animal kingdom in a few major groups called phyla, which is the plural form of phylum. It so happens that the leeches belong in one phylum and the ticks belong in a very different phylum. The leeches are annelids of the phylum Annelida. All the members of this group are true worms with segmented bodies. The leech's cousins include the earthworms, who do so much to enrich the soil. However, the leech has simplified eyes and a sucker at each end of his wormy body.
Assorted leeches lurk in most soggy swamps and muddy streams. There they attach themselves to fishes, turtles and people who happen to be in the water. The tail sucker is used to hold on to the victim while the sucker at the head end draws out the blood. A 2 inch leech can gorge enough at one meal to swell to a bloated 4 inches.
The itchy ticks have bodies like oval bags, eight legs with claws to grip their victims and sharp, sucking beaks. They are classed in the huge phylum Arthropoda, which means the animals with jointed feet. Their distant cousins are the teeming insects, and their closer relatives are the spiders.
Every continent has an assortment of ticks except Antarctica. Most of the ticks are barely big enough to be seen, though the largest species is an inch long. Many feed on liquid blood, some on plant juices and a few dine on decaying materials.
The arthropods with their complicated heads and legs are rated as far more advanced than the simple wormy annelids, which means that the bloodsucking ticks and the bloodsucking
leeches are not even distantly related.
In bygone days, it was thought that a sick person needed to lose some blood. And, of all things, doctors used leeches to treat their patients. Nowadays, we know that a patient needs plenty of healthy blood. What's more, we know that both leeches and ticks carry germs and sometimes deadly diseases.