Milwaukee Public Museum

by Joan P. Jass

EDITOR'S NOTE: This article is reprinted without illustrations from LORE magazine, a benefit of museum membership. ©1996 Milwaukee Public Museum, Inc.

As the plane descended through the broken cloud cover of the late afternoon, I could see that we were entering a wide valley surrounded by green, forest-covered slopes, obscured in part by drifting wisps of clouds. To be, this was the first exciting vista of "The Tropics"--an exotic locality in which to be spending the next ten days of late February and early March collecting invertebrates for the museum.

More specifically, we were about to land at Juan Santamaria International Airport just outside San Jose, the capital of Costa Rica. San Jose, along with the large cities of Alajuela, Heredia and Cartago, lies in the broad valley known as the Meseta Central, where over two million of the citizens of this Central American republic reside.

It was those surrounding slopes that were the chief topographical feature influencing the contrast between the two major life zones where we would be doing most of our collecting:the lowland wet forest of the northeast and the lowland dry forest of the northwest. Winds from the northeast force clouds to drop their moisture on the Atlantic coastal plain as they rise and cool when they meet the slopes of the interior. The lowland dry forest of the northwest lies within the rain shadow of these mountains,meaning that air masses which have crossed the interior ranges have released all their moisture as rain before they ever blow across this resultingly arid portion of their transect of the country.

Lying only 8-11 degrees north of the equator, Costa Rica encompasses tropical habitats as well as those which, because of complex interactions of topography and climate are outside the range of conditions we usually think of as "tropical." The Meseta Central itself of example, a highland plain surrounded by mountains, maintains an ideal "temperate" climate because of its altitude with temperatures in the 70s year round.

Seasonality in this part of the world is marked by differences in rainfall, with a dry season occurring during the months of our northern winter. The beginning of March was the date for Costa Rican children to return to school, ending their "summer" vacation.

The climatic factors which create these tropical seasons also account for features on observes in the vegetation. In the San Jose vicinity, tall Erythrina trees were covered with pink-orange blooms on otherwise bare branches. Limbs of the other trees covered with a thick blanket of epiphytes were not lush green but brownish, waiting for the reviving rains to come in several weeks. Lushness dominates the surrounding slopes, which are evergreen, some moisture being constantly supplied to those heights throughout the year from the ever-present clouds.

Vegetational diversity is a hallmark of the Costa Rican landscape. In fact, the impact of it is so great as to be almost dazzling to the first time visitor. On the large scale, this means that one feels that practically wherever you are,you could go twenty miles in another direction, and you would be in a different life zone with its own set of plant species and correspondingly unique aspect to the features of its overall vegetational appearance.

On the smaller scale, such diversity can mean that even within one life zone, so many different leaf shapes and sizes, vines and cacti, tree trunks, pods and flowers, epiphytes, ground vegetation, ferns mosses,grasses--all present themselves to your eye in such variety and profusion as to elicit the temporary daze of visual saturation--similar to the state of a museum visitor who tries to see it all in one visit.

All the reasons for this great diversity occurring within one small country, in area about the size of West Virginia, have been and continue to be an exciting challenge for scientists to figure out. Costa Rica's internal topographic complexities but one aspect to the explanation. Another aspect, which affects climate as well as geological history, is the geographic situation of the country in a position where both Central and South America influences are strong.

With all this potential for disorientation for the newcomer attempting to comprehend a land where distances and ecological divisions present such a novel and complex array of choices for exploration, I was fortunate to be arriving in the company of Dr. Allen Young, Who has conducted numerous research projects in Costa Rica over the past fifteen years and knows the country well. We would be joining a third member of the museum staff, Susan Borkin, who had arrived in San Jose the previous week. Our trip was being made possible through the generous funding of the MPM Friends of the Museum.

Besides conducting his own research--on many topics including butterflies, cicadas, and cacao-pollinating midges--Allen had been bringing back numerous specimens for the museum's collections from a wide variety of other animal groups--spiders, scorpions, millipedes, centipedes,crustaceans and mollusks, to name but a few. Now was the opportunity for Sue and me to see for ourselves the collecting sites from which these specimens had originated as well as to try our own hand at doing some of the collecting.

In the ten days to follow, we were to sample quite a few of those varied Costa Rican habitats: forest remnants bordering agricultural fields in the Central Valley, cloud forest along the highway heading northeast over the mountains from San Jose, lowland wet forest of the Atlantic coastal plain, fresh flowing waters of the Rio Titimbina, lowland dry forest of northwestern Guanacaste Province, and the sandy Pacific shore at Playsa del Coco.

General collecting of invertebrates is in actuality a not very realistic statement of our goal. The tremendous variety of invertebrate animals, which in size alone run the gamut from protozoan to giant squid, demands selectivity from the collector. Our more specific collecting goals were therefore to be: for Su and Allen, chiefly the acquisition of butterflies and moths for our MPM collection as well as life history information for selected members of this group and, for me, primarily collecting spiders by sweep netting.

Over the years, in their efforts to effectively gather a representative sample of the fauna of a particular site, collectors have devised some fairly ingenious methods for achieving this goal. These range in complexity from traps and extractors which take pages detail and diagrams to describe to rather simplistic ones like sweep netting. The net I used was canvas with a fifteen inch diameter mouth, a thirty inch long cone-shaped bag and a yard long lightweight aluminum handle. To use the net one sweeps it back and forth through the vegetation, dislodging many spiders and other arthropods which are swept into the bag along with bits of vegetation and debris. This mixture must be sorted through to isolate potential specimens from unwanted material. Any spiders are dispatched with ethyl alcohol dispensed from a plastic squeeze bottle, and then the sweep process begins again.

Because of the well-known abundance of their insect prey, one expects a corresponding high population of spiders in the topics. In the dry season these populations are down somewhat and concentrated in the moister habitats. While a resultant absence of mosquitoes was for me a definite plus, I wondered whether spider populations, whose members generally lack the highly sclerotized cuticle of many insect which protects them from dehydration, respond with a relatively greater drop in numbers to the dryness of the season.

This is not to say that spiders were really scarce. There were plenty of large-bodied Silver Argiopes on trailside vegetation, huge Golden Silk Spiders with thick-stranded webs under the eaves of the Tirimbina guest house and spun between shrubs on either side of the forest paths, sun-loving Jumping Spiders poised on leaves and stems in clearings to pounce on unsuspecting prey or even stalking moths attracted to the artificial light we set out for night collecting.

One collecting technique I found especially enjoyable was the use of a headlamp for night collecting. While I had read that one could spot the glowing eyes of spiders as they reflect the headlamp's beam, I had never experienced it for myself and was admittedly somewhat dubious as to how easy it would be to detect reflections from the tiny eyes of a spiders. Not only was it easy to do, it was a spectacular experience to witness the many diamond- like sparkles of spider eyes in the dark. An added bonus to this aesthetic delight was the fact that the wolf spiders responsible, which in the daylight were usually swift enough to escape my attempts at capture, remained transfixed in the beam of light as I approached,making collecting easy.

Field work is of course just the initial step in the process of adding specimens to the museum collections. While acquiring material in the field, one usually needs to attempt to maximize use of the storage space available. Compact packing of specimens and their containers will allow the return of the most in the least amount of packaging, within the limits of safety for the specimens inside.

Back at the museum, processing of the newly acquired material begins. Now a different goal assumes priority. Rather than frugality in use of space, long-term preservation of the specimens becomes the primary determinant for their treatment. So everything is unpacked, sorted carefully, put into permanent containers with ample amounts of preserving fluids where necessary, and labels with detailed locality data. Then the inventory can be made which allows the hundreds of specimens to be accessioned into the collections, thus becoming the legal property of our museum.

The fun of finding out the identities of the specimens I collected comes only after a sometimes difficult and usually lengthy (continuing over months or even years) additional process. In this process I am aided by zoologist I have not met but know only through correspondence. The idea is to arrange loans of our specimens to the appropriate experts who, in the interest of examining new material possibly pertinent to their own research, are willing to return the specimens to us fully identified upon the completion of their studies. Over the years, we have built up a file of such contacts so that we now can rely on the North Carolina museum's millipede expert, the Harvard orb-weaver specialist and others like them for this vital service.

It is only then that such specimens take on their importance as bits and pieces of information about the biological world. For many tropical groups, the fauna is so poorly known that sometimes not even the experts have seen these species before. Even those that are known have frequently been described from only a few specimens and every additional one adds new information on the morphological variation, the habitats and geographic range occupied by animals we have just begun to know.

From a tiny crab collected at the Guanacaste beach of Playas del Coco, which turned out to be quite familiar to the identifying expert, I learned a great deal about the range of morphological variation which such creatures can display. This crab was standing right at the edge of the waterline when I saw it, looking as though it would easily be swept away by the next incoming wave, a precarious situation for so frail a creature, I thought.

Back at the museum, this tiny crab remained a puzzle for me. Using the references available, I just could not seem to fit it into any crustacean family, despite some fairly distinctive features such as large eyes and placement of its last pair of legs in a dorsal position. Using these features I made a stab at a possible family ID and was fortunate enough to find an expert in that group who was willing to examine our specimen. The letter which I had received in response to my initial request for help in identification included a generous offer to refer the inquiry to other specialists in that lab if necessary. So, since our total sum of specimens from the site would fit into the same small shipping container, I impulsively sent all of the crustaceans collected off to the experts at the University of Southern California lab, not just the one I had originally requested permission to send.

Within an astonishingly fast period of two weeks I had all my specimens back fully identified. There was a mole crab species that had been collected from Playas del Coco previously, a small hermit crab identical to those in a series that Allen had brought back from that locality in 1975, and two with squarish bodies that were just different sizes of the same ghost crab. But--the big surprise for me--the tiny big-eyed one was a ghost crab too, an immature stage called the megalops. Upon reading up on the megalops stage of crabs, I found that it had fooled early naturalist also, who placed it in its own genus Megalops and failed to recognize this strange-looking individual as bearing any relationship to the adult crabs in the vicinity. The difference in behavior at this stage is significant too; the megalops is a strong swimmer, with appendages suited for that purpose, in contrast to the bottom-dweller it will transform into as an adult. So, it had not been in the precarious situation that I had supposed when I first spotted it at the water's edge.

Having failed to make the connection between these now well- known facts of a crab's life history and the tiny creature I was struggling to identify, I was doubly grateful for the sharing of scientific knowledge by generous experts who had not only provided the corrected identity of this individual but also given me a firsthand insight into the life history changes represented by the three Playas del Coco ghost crab specimens which are now part of the MPM invertebrate collection.