Swarms of Butterflies and Swallows

     Many times I have driven along country roads in Lancaster County, Pennsylvania farmland during August and September and been entertained by fluttering multitudes of yellow sulphur and cabbage white butterflies among the lovely red clover and alfalfa blossoms in hay fields and dozens or scores of local and migrant barn swallows, tree swallows and purple martins, which are another type of swallow, swooping low over those same beautiful fields.  Those abundant butterflies and swallows are both seeking food, sugary nectar in the flowers for the butterflies and flying insects for the swallows.  
     Every late summer, flowery hay fields are full of those butterflies and swallows that create much beauty and interest to those who experience them.  The yellow sulphurs are, by far, the most abundant of these five species in Lancaster County hay fields.  Many alfalfa and red clover fields shimmer with thousands of yellow wings as the sulphurs continually flutter from bloom to blossom.  The white-winged cabbage white butterflies are also common flitting among the flowers, and offering a spangling contrast of color among the yellow sulphurs.
     The sulphurs are native to North America, but the cabbage whites are originally from Europe and Asia.  Both these species, however, long ago adapted to agricultural practices and crops, which is why they are so abundant today.
     Sulphur caterpillars adapted to eating the abundant clover and alfalfa, among other plants.  And cabbage white larvae consume plant members of the mustard and cabbage families.  The caterpillars' adapting to eating cultivated crops also led to their species' being abundant in numbers today.
     Of the few generations of both species during the warmer months each year, the last generation spends the winter as pupae in the ground.  Next spring they emerge as winged adults. 
     There are other kinds of butterflies commonly in red clover and alfalfa fields during July, August and September, including monarchs, silver spotted skippers, meadow and great frittilaries, and tiger, black and spicebush swallowtails.  Each of these species has a reason to be common in hay fields.  Monarch caterpillars feed on milkweed leaves that grow commonly along rural roads.  Skipper larvae eat soybean leaves.  Soybeans are a big crop in Lancaster County.  Frittilary larvae ingest violet foliage, which is common in fields and along roadsides.  Tiger swallowtails come out of nearby woods to visit clover and alfalfa flowers because their caterpillars consume tree leaves.  Spicebush swallowtails also come from local woods because their young eat spicebush and sassafras leaves which are abundant in woods and along rural roads respectively.  And the larvae of black swallowtails ingest parsley leaves in country gardens.        
     Sweeping swiftly across the sky, and over hay fields and other cropland, without collision among their relatives, swarms of barn swallows, tree swallows and purple martins pursue flies and other kinds of flying insects as those birds slowly drift south for the winter.  And like hordes of butterflies in hay fields, these swallows are entertaining to watch careening in and out among their fellows.  The swallow species have formed flocks prior to their migrating south to avoid the northern winter and find a reliable source of flying insects to feed on.  Sometimes each species is in its own company, but other times they travel in mixed groups of scores or even hundreds.
     All these attractive swallow species have long nested in North America.  Barn swallows nested in the mouths of caves, but now raise young in barns and under bridges.  Tree swallows hatch offspring in abandoned woodpecker holes and other tree cavities, and in bird houses erected for them and eastern bluebirds.  And martins rear offspring in hollow, erected gourds and apartment bird houses which substitute for standing dead trees with several hollows in them.  These species of swallows' adapting to human-made habitats has bolstered their populations tremendously, and has also increased our potential for enjoying their migration gatherings and flights.  And these swallows cut into populations of flies, mosquitoes and other pesky, even dangerous, insects.
     This late summer, or succeeding ones, watch for swarms of butterflies and swallows in and over red clover and alfalfa hay fields getting their respective foods.  Those butterflies and swallows are always entertaining to see going about their daily business of food gathering.