Last time on A Moment of Science, we found that lobsters and crayfish communicate by shooting streams of urine into each others' faces. Now, we look at urine signaling from the receiver's end.
When shooting out urine streams, the crustaceans direct the stream toward the target with fan-like appendages located near their mouths. These "fan organs" give the signal sender very precise control over where the urine stream goes. They can accurately direct the stream anywhere within a 180 degree range in front of them. The same fan organs can also be used to direct chemicals into the mouth of the crustacean.
In a watery environment chemical signals can quickly diffuse away. If you want to know who else is nearby, and whether they are a potential mate or dangerous rival, it's critical to know who and where a signal came from. A team of English Biologists discovered that crayfish can use their fan organs to follow underwater chemical trails, like bloodhounds following scent trails. The fan organs move water across receptors near the crayfish mouth that compare how concentrated the chemical is in the water.
The crayfish are so good at following underwater trails that scientists are working with NASA to develop small autonomous robots modeled after the crayfish. The odor-tracking robots can detect small concentrations of chemicals and trace it back to the source by following a concentration gradient, just like crayfish. Small robots like that could really be useful in underwater rescue efforts, locating sources of chemical spills or pollution.