Signs of Spring: May Flowers, Horseshoe Crabs and Astronomy Charts

May flowers, the season of the horseshoe crab and summer astronomical occurrences for 1993.


| April/May 1993



137-020-01

Breeding season for horseshoe crabs is a sign of spring.


ILLUSTRATION: MOTHER EARTH NEWS STAFF

With all the rapid changes in nature throughout springtime, I wonder if four seasons are enough. After all, seasons are time periods characterized by a set of events or states in nature that are distinctly different from those of the previous time period. Considering the many changes between March and April alone, shouldn't we add in an extra season during this time? It might be nice to have something like the six seasons of the Elves, which appear in stories written by fantasy writer J.R.R. Tolkien. Between winter and spring comes "stirring"; between autumn and winter comes "fading." After all, in much of the United States, March (and at least some of April) are still extremely cold, the trees are not fully leaved, and the time of maximum blooming is still to come—conditions we hardly associate with spring.

On the other hand, we must be careful not to distort reality by forcing it into too many organizational schemes. Many events in the natural world are not sudden. Like the cold spells which persist in March and April, these events just grow fewer and less severe. There's also a positive side to having four seasons; it makes the details of each particular one more extreme. So as the cycle of seasons rolls around again, the nature watcher can search for the familiar details—patterns in nature and life—and then delight in the recognition of seeing them.

Bringing May Flowers  

Over 600 years ago, Chaucer opened his Canterbury Tales "Whan that Aprille with his shoures sote [sweet]/The droghte [drought] of Marche hath perced [pierced] to the rote [root]..." Everyone knows about the infamous April Showers, but does the saying actually hold up to meteorological scrutiny?

Yes. Of course the amount of rain you see depends on what part of the country you live in, and showers seem to be a phenomenon mainly of Eastern states. Keep in mind that I'm not talking about the amount of precipitation—March would probably win hands down—but the frequency of come-and-go sprinkles and downpours. Through winter and March, low-pressure systems tend to produce widespread, not localized areas of precipitation. But in April, the higher sun of longer days starts heating the ground significantly, causing warm air near the surface to expand and rise up into still-cold air aloft: this "convection" makes cumulus clouds puff up and grow enough to produce showers and thundershowers. As the year progresses, convective activity by no means stops, but a variety of factors usually prevents it from giving rise to showers on as many days as in April.

The Living World  

In addition to blooming flowers, May brings us the Season of the Horseshoe Crab, when the crabs make their big coming out. This "living fossil," which looks just like a walking helmet, has virtually no living relatives in the animal kingdom. From Maine to Mexico, you can see them traveling the Atlantic beaches. (The only other place the horseshoe crab exists in the entire world is Southeast Asia.) Perhaps it's strangest characteristic—aside from its blood, which is a rich copper blue—is its extra set of eyes, which can see in ultraviolet light. As for its most useful characteristic, it would have to be the strange chemical, limulus lysate, which is found in the horseshoe crab's blood. This life-saving chemical is used to test whether or not medicines have become contaminated with bacterial toxins.

This strange animal also provides an essential feast to several species of migrating birds in May. The primary location of this event is in New Jersey and the Delaware shores of Delaware Bay for a brief period in late May. Horseshoe crabs are then seen in enormous numbers on the beaches, because this is when the females males lay eggs for the males to fertilize. Enter hundreds of thousands of birds, most in the midst of immensely long migrations, all looking for horseshoe crab eggs and overturned horseshoe crabs. One type of sanderling (a small type of shore bird), called the Red Knot, travels 9,000 miles, from as far south as Tierra Del Fuego in Argentina on its way up to northern Canada.





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