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Dr. Dean W. Blinn

Montezuma Well

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Once the protection of darkness sets in, the disadvantages of being seen by a hungry predator are reduced, at least so it seems! As the sun sets, an exciting sequence of biological events begins. Around the margins of the Well, hungry daddy long leg spiders and assorted tarantulas scamper over the damp soil in search of food. Numerous bats and swallows leave the crevices and caves in the surrounding cliffs to feast on a variety of insects. Even the resident Great Horned Owl takes advantage of the many small mammals that use the protection of darkness to feed and hopefully reduce their chances of being seen by a hungry predator.

A number of similar events also occur in the water. First, the resident muskrats leave their mud burrows along the shore of the Well and swim into the aquatic plants to feed. Also, many of the amphipods swim to the surface of the open water and gorge themselves on algae by trapping these tiny plants in specialized feeding hairs near their mouth (see illustration below). The amphipods can no longer be fed upon by ducks and turtles because they can't be seen, but they must escape from a new predator.... the leech.

Soon after sunset, the leeches leave their soft mud tunnels and slowly swim to the surface and feed on the abundant amphipods near the water surface. Fortunately, the leeches do not need to see the tasty amphipods, but instead hunt their food by using tiny sensory hairs (pictured below) to detect the water vibrations produced by the swimming amphipods. The amphipod's only defense is to curl up and expose the spines found on their backs (see above picture of amphipod).

Once the amphipods have collected the algae on their feeding hairs and have filled their guts, they disperse into deeper water and also into the aquatic plants located around the margin of the Well. This movement usually occurs several hours after sunset; the leeches follow in pursuit! Hungry leeches may track down additional amphipods in the vegetation, while leeches that are full probably return to their soft mud tunnels at the bottom to conserve energy and digest their evening meal. A typical evening meal for each leech consists of about 14-20 amphipods.

Not only do the amphipods need to be aware of leeches sneaking up from below, but they also need to be concerned about the water scorpions that swim out from the vegetation. These water scorpions swim near the surface and feed on the amphipods with their piercing beaks. This cat-and-mouse game between prey and predator is most active around twilight but continues until sunrise after which all is calm in the surface waters of Montezuma Well.

Day in the Well Montezuma Well Man at the Well