Insects Encounters in Costa Rica

 

Reticulated Lubber Grasshopper (Romalea reticulata).  
The small, nonfunctional wings identify this grasshopper as a nymph.
Turrialba, Costa Rica. 

The tropics are renowned for their biodiversity.  Astonishing forms of plant life, dazzling birds and remarkable mammals are overwhelmed by the sheer variety of insects.  Insects exhibit an astonishing range of sizes, shapes, colors and show amazing behaviors.  Costa Rica, a country about the size of West Virginia, is estimated to have over 250,000 species of insects.  We recently visited Costa Rica on a bird watching trip led by Epic Nature Tours.  Even though birds were our main interest we were constantly drawn to the beauty and drama of the insect life. 

Stick Insect (Trychopeplus laciniatus) blending into
a mossy background.
Guayabo National Monument, Costa Rica. 

Trychopeplus laciniatus in the hand.
Guayabo National Monument, Costa Rica. 

One day while hiking in a rainforest our guide pointed to a tree trunk covered with mosses and lichens.  There crawling slowly over these tiny plants was a barely visible walking stick Trychopeplus laciniatus.  This stick insect is green with mossy decorations on its body and legs that allow it to blend perfectly with the background vegetation.  Trychopeplus laciniatus feeds on leaves, particularly those of epiphytic orchids and uses its amazing camouflage to hide from predators. 

Leaf Cutter Ants (Atta sp.)
Turrialba, Costa Rica. 

Winged queen Leaf Cutter Ant.
Savegre Valley, Costa Rica. 

Leaf Cutter Ants (Atta sp.) are among the most abundant insects in Costa Rica.  We constantly saw them marching along their well cleared trails, holding pieces of leaves over their head.  These ants live in huge colonies with populations of up to 8 million.  A single queen is the mother to all these ants. New colonies are established when a winged virgin queen takes her nuptial flight.  She mates with winged males and stores enough sperm to populate a new colony that could thrive for years. 

Video of Leaf Cutter Ants walking along their trail. 

Turrialba, Costa Rica. 

Video by Diane Coggin. 

Leaf Cutter Ants do not eat the leaves they cut.  The ants carry leaf fragments to their underground colony.  There the Leaf Cutter Ants chew the leaves and inoculate them with a fungus that is the sole food for the ant colony.  The ant and the fungus have a mutualistic relationship with the ants providing the fungus with nutrients (leaves) and the fungus giving ants their food supply.  There are 18 species of Leaf Cutter Ants in the genus Atta.  All are found in the New World and each cultivates its own species of fungus. The ant-fungus relationship is considered a form of agriculture and has been going on for over 50 million years, vastly longer than human cultivation of crops. Neither ant nor fungus can survive without the other.     

Female Aloeus Ox Beetle (Strategus aloeus). 
Turrialba, Costa Rica. 

Female Aloeus Ox Beetle. 
Turrialba, Costa Rica. 

Beetles are the most abundant of all the insects and we encountered some of this beetle diversity on our travels.  The Aloeus Ox Beetle (Strategus aloeus) is impressively large and dark.  The males have three horns they use for fighting while females lack large horns.  The larva of the beetle live underground and feed on the roots of plants.  Adult Aloeus Ox Beetles eat mainly flowers and fruit. 

Isotes sexpuncta.
Savegre Valley, Costa Rica. 

While hiking in the cloud forest of Savegre Valley we found a small orange beetle with black spots (Isotes sexpuncta)  sitting on a leaf.  This beetle is found only the the highlands of Costa Rica and belongs to a group called skeletonizing leaf beetles.  These beetles eat the soft tissue of leaves and leave behind only the leaf veins, the skeleton.  

Soldier Beetle (Chauliognathus sp.).
Tapanti National Park, Costa Rica. 

Another attention-grabbing beetle was a black and yellow Soldier Beetle (Chauliognathus sp).  These large beetles, with their bold color pattern were advertising their unpalatability to predators. 

Reticulate Lubber Grasshopper.
This is an adult identified by its wings. 
Turrialba, Costa Rica.

We found Reticulate Lubber Grasshoppers (Romalea reticulata) eating grass leaves on the slopes of the Turrialba Volcano. These grasshoppers are impressively large (over 3 inches long) and black with purple markings on the wings, legs and body.    

Tarantula Hawk (Pepsis sp.).
Lankester Botanical Garden, Costa Rica. 

The most dramatic insect interaction we saw involved a Tarantula hawk (Pepsis sp.). This large wasp has a black body, orange wings and yellow antennae.  The Tarantula Hawk was hunting the even larger Red-thighed Bromeliad Spider (Cupiennius coccineus).  This dangerous pair of arthropods faced off in a duel to the death on the peaceful grounds of the Lankester Botanical Garden in Cartago.  As an adult, the Tarantula Hawk feeds on nectar but causes searing pain if you are stung.  In fact, it is rated a 4 on the Schmidt Pain Index.  Dr. Justin Schmidt spent his career studying bites and stings from arthropods. This dedication to his research included allowing these animals to bite and sting him.  The Schmidt Pain Index runs from 0 (no effect on humans), to 2 (bee sting), to 4 (excruciating).  Only two insects are rated as a 4 on the index and the Tarantula Hawk is one.  Dr. Schmidt described the sting of a Tarantula Hawk as “Blinding, fierce, shockingly electric. A running hair dryer has been dropped in your bubble bath.” 

Red-thighed Bromeliad Spider (Cupiennius coccinea).
Lankester Botanical Garden, Costa Rica. 

The spider in this drama, a Red-thighed Bromeliad Spider, had a leg-span of about three inches and was hunting across a lawn.  These spiders can also deliver a painful bite but nothing like the pain of a Tarantula Hawk sting.  As the spider was walking the low-flying Tarantula Hawk spotted it.  The wasp made repeated attacks.  The spider would rare up, showing its fangs and waving its front legs, but the Tarantula Hawk would fly around to the side or back of the spider.  Then the wasp was able to deliver a sting to the spider.  Within moments, the powerful neurotoxins paralyzed the Red-thighed Bromeliad Spider.  The wasp then began to drag the spider across the ground. We followed the Tarantula Hawk for over 100 feet before we had to leave.  The Botanical Garden was closing and staff would not wait for us to watch the end of the encounter.  The fate of that Red-thighed Bromeliad Spider was to be paralyzed and buried alive, with a Tarantula Hawk egg attached.  After the egg hatched, the wasp larva would eat the spider alive, consuming the nonvital parts first.  After several weeks of development an adult Tarantula Hawk would emerge and begin its spider hunt.    

Tarantula Hawk hovering over Red-thighed Bromeliad Spider.
Lankester Botanical Garden, Costa Rica. 

Tarantula Hawk stinging Red-thighed Bromeliad Spider.
Lankester Botanical Garden, Costa Rica.

Tarantula Hawk dragging paralyzed
Red-thighed Bromeliad Spider.
Lankester Botanical Garden, Costa Rica. 

The tropics exhibit a dazzling diversity of insects.  On our trip to Costa Rica we saw just a handful of the country’s insect marvels. Sitting at home and recounting these encounters makes me think of the small wonders and the life-and-death struggles that play out in the tropics. 

The Mallard Continuum

 

Male Mallard (Anas platyrhynchos).
Rowan County, North Carolina. 

Mallards (Anas platyrhynchos) are the ducks that people think of when they think of ducks.  Mallards are large ducks with a wingspan of about 3 feet and weigh about 3 pounds. Males have an iridescent green head, a white collar and maroon breast.  Females have a more muted color pattern of mottled brown with an eye stripe.  Males Mallards have a yellow beak with a black tip and females have a brown beak. Both male and female Mallards have a bright patch of iridescent blue feathers on the wing called a speculum.  The speculum has white borders and is visible when the ducks are in flight but is harder to see when they are not airborne.  Mallards also have white on their tail feathers. 

Female and male Mallards.
Buncombe County, North Carolina. 

Female Mallards give the classic quack call while males have a quiet, raspy call. They belong to a group of ducks called dabblers because they feed in shallow water by tipping their tails in the air and collecting plants and small animals from the bottom with their beaks.  Mallards are native to most of the northern hemisphere and have been introduced to many locations in the southern hemisphere. 

Male and female Mallards feeding.
Buncombe County, North Carolina. 

                                             

Video of Mallards mating. 
Rowan County, North Carolina.

While male Mallards are unmistakable, females Mallards look very similar to other species of ducks,  in the genus Anas, including the males.  American Black Ducks (Anas rubripes), Mottled Ducks (Anas fulvigula) and Mexican Ducks (Anas diazi) all strongly resemble female Mallards.

American Black Duck (Anas rubripes) in flight.
This duck's dark body, lighter head and violet speculum are all visible.
Alligator River, National Wildlife Refuge, Dare County, North Carolina. 

American Black Duck in flight showing white undersides of wings.
Alligator River National Wildlife Refuge, Dare County, North Carolina. 

American Black Ducks are widespread in eastern North America.  They breed from northern Canada and the upper Midwest and down to North Carolina.  The northern-most America Black Ducks migrate in winter and can be found as far south as the gulf coast from Louisiana to north Florida. America Black Ducks look like very dark female Mallards.  Their heads are lighter than the body, the undersides of the wings are white, and the speculum is violet.  American Black Ducks are the largest ducks in the genus Anas and readily produce fertile hybrids with Mallards.  

Female and male Mottled Ducks (Anas fulvigula). 
West Delray Regional Park, Palm Beach County, Florida.

Mottled Duck showing iridescent blue speculum.
Green Cay Wetlands, Palm Beach County, Florida. 

Mottled Duck.
Green Cay Wetlands, Palm Beach County, North Carolina.  

Mottled Ducks are found throughout much of Florida and north along the Atlantic coast to South Carolina.  A separate subspecies of Mottled Duck ranges from coastal Alabama to Texas and northern Mexico.  Mottled ducks are a little lighter than American Black Ducks but darker than female Mallards.  They have a blue speculum and male Mottled Ducks have a yellow bill while females have greenish bills.  Both males and females have a black spot at the hinge of the bill.  Mottled Ducks also readily produce fertile hybrids from mating with Mallards.

 

Mexican Duck (Anas diazi) displaying its blue speculum.
Willcox Playa, Cochise County, Arizona.

Mexican Ducks range through much of Mexico but can also be found near the border from Texas to Arizona.  They are very similar in appearance to female Mallards but lack white tail feathers and the white border on the speculum is narrower than on the Mallard.  Like American Black Ducks and Mottled Ducks, Mexican Ducks can hybridize with Mallards.

Female and male Mallards.
Rowan County, North Carolina. 

Why do all these ducks look like female Mallards?  All four of these species are closely related. The evolutionary ancestor of this whole group probably looked like the female Mallards of today.  Genetic studies tell us Mottled Ducks diverged from Mallards about 390,000 years ago, Mexican Ducks became a distinct species about 325,000 years ago, and Black Ducks and Mallards separated only 180,000 years ago. While these are long stretches of time, they are but an instant in evolutionary history.  These ducks are all still in the process of becoming genetically isolated from each other.  

Male Mallard
Rowan County, North Carolina. 

Another question is why the males and females of Mottled Ducks, Black Ducks and Mexican Ducks look similar, but in Mallards the males and females look dramatically different.  For some reason, in the Mallard line, the females favored flashily colored males.  Over time a process called sexual selection produced the extravagant males we see today.  Why this has not happened in other ducks of the Mallard continuum is a mystery.