The 17 Year Itch

That sound you hear isn’t the Six Million Dollar Man using his bionic powers. It’s cicadas by the billions. Every year, at least a few cicadas emerge during late spring and serenade us with their mating call. Chunky and scary looking, these insects are totally harmless but to me at least, just hearing them makes it feel a little hotter and muggier. 

This year is a little louder than most. Brood X, the largest brood of periodical cicadas, is emerging after 17 years underground in the larval stage. They’ve been tapping into tree roots during that time and now that they’ve reached adulthood they’re ready to go out in a blaze of noisy glory. They'll mate soon, lay their eggs in the tree tops, and die. When the eggs hatch, the larval cicadas will drop from the tree, burrow into the ground, and start the timer on another 17 years.

Expect it to be a little louder than usual in the Northeast
(From "This Is Spinal Tap")

All those bugs means not just a lot of noise, but also a lot of food for just about everything. The reason cicadas emerge by the billions is to overwhelm their predators’ stomachs. The strategy is that lots of cicadas will get eaten, but based on sheer numbers, many will survive to continue the life cycle for another 17 years. 

Periodical cicada (NPS)

Speaking of 17 years, why such an odd number? It’s another evolutionary strategy. What other critter can you think of with a 17 year life cycle? It reduces the risk of broods emerging during a population boom for a predator species. As a double failsafe, broods have stragglers that emerge either before or after the 17 year period.  Most are within a 13 to 21 year period. It gives the brood a better chance of survival in the event that the 17th year is a boom year for predators. 

Molting cicada (Baltimore Sun)

I've never seen a cicada coming out of its shell. Like all insects, they have a hard exoskelton, and immediately after emerging they molt. From what I'm being told, people all over are finding a lot of those shells on tree trunks and other surfaces. I haven't seen any yet this year, but I haven't been able to get outside much other than a birding expedition to New Jersey which you can read about later. This week's information comes from the University of Connecticut. 

Species of the Month

Halloween is just around the corner. Traditionally, we examine a spooky critter with a connection to Halloween for the Species of the Month. This year let’s try something different. There’s nothing scary about a ghost crab, but its name fits the season. 

Ghost crab (Science Magazine)

Scientific name: Ocypode quadrata 

Kingdom: Animalia (animals)

Class: Malacostraca (soft-shelled crustaceans)

Order: Decapoda (ten-footed crustaceans)

Range: Rhode Island to Brazil 

Habitat: Ocean or estuary beaches, from the tide line to the dunes 

Lifespan: 3 years 

Diet: Bean clams, mole crabs, sea turtle eggs and hatchlings, organic detritus 

Predators: Shore birds, gulls, raccoons 

Conservation status: No special protection

Other info: Ghost crabs are small, nocturnal crustaceans. They grow to about a two inch carapace (back shell) with long legs and eye stalks, and their claws are uneven sizes. Ghost crabs hatch from an egg in the ocean and go through six larval stages before developing into adult crabs. Unlike other crabs that can only mate when the female is molting, ghost crabs can and do mate at anytime after reaching maturity which is usually after a year old.  

Juvenile ghost crab (NPS)

Ghost crabs live in burrows in the sand. They plug the holes during the day and emerge at night for feeding and mating. Mating occurs near the male’s burrow. They travel several feet per night and may not return to the same burrow. Occasionally they will go into the water to wet their gills; they are also capable of absorbing water from the sand into their gills. 

Ghost crabs can be used as an indicator species to monitor the health of their habitat. Populations can be easily estimated by counting burrows. Knowing the status of the crab population can tell what kind of impact human activities are having on the ecosystem overall. Off road vehicles and coastal development are the biggest challenges we give them. 

A pair of ghost crabs (NPS)

Once again this week's information comes from the Animal Diversity Web at University of Michigan. Next week is a rerun. We'll have fresh content after Halloween. Stay tuned!

Species of the Month

Don’t laugh at November’s Species of the Month. Although it lends its name to the fiction hometown of the Griffin family in TV’s The Family Guy, the northern quahog (pronounced co-hog) is a real animal. A species of clam, it was likely eaten at the first Thanksgiving in 1621. The Pilgrims neglected to save a menu for posterity, so we’ll never know for sure. Will your Thanksgiving meal include any seafood? 

Northern quahog (NOAA Fisheries)

Scientific name: Mercanaria mercanaria 

Kingdom: Animalia (animals) 

Class: Bivalva (bivalves) 

Order: Veneroida (saltwater and freshwater molluscs) 

Range: East coast of North America from Gulf of St. Lawrence to Gulf of Mexico 

Habitat: Estuarine intertidal mudflats 

Lifespan: 30 years or more, a separate Arctic species was found to be 507 years old 

Diet: Zooplankton and phytoplankton 

Predators: Moon snails, oyster drills, whelks, rays, skates, shorebirds, humans 

Conservation Status: No special protection. 

Northern quahog (Chesapeake Bay News)

Quahogs are commercially harvested. In addition to a food source, they act as a natural filter by feeding. They filter feed through a siphon that extends from the shell. Plankton and pollutants go in, clean water comes out. Quahogs are mobile, although they don’t move much. A single foot at the base of the shell holds it in place in the mud or sand and can quickly dig in to avoid predators. It can also be used to move laterally. Quahogs reproduce by releasing sperm and egg cells into the water, where they randomly meet and fertilize. Within two weeks, the quahog larvae have formed a foot and shell and anchored to the substrate. Ocean currents aid in fertilizing the eggs and dispersing the larvae. This week's information comes from University of Michigan's Animal Diversity Web.

The Shell Game

Ever wonder what the difference is between a turtle and a tortoise? They’re both shelled reptiles so is it all just a name? Not exactly. All tortoises are turtles, but not all turtles are tortoises.

Desert tortoise (NPS)

A tortoise is a turtle that lives exclusively on land, while most (but not all, remember there’s always an exception) turtles spend most of their time in the water. Because of the lifestyle differences, turtles have webbed feet and tortoises don’t. And of course sea turtles, who only come on land to lay eggs, have flippers instead of legs. Tortoise shells are generally taller, while turtles have a flatter, more aquadynamic shell design.

Box turtle (NPS)

Loggerhead sea turtle (USFWS)

Now that you have that down, let’s introduce the terrapin. Terrapins are mix of the landlubbing tortoise and seafaring turtle. They spend half their time on land, half in the water. They have a more streamlined shell than a tortoise, yet it’s taller and rounder than a turtle’s. 

Diamondback terrapin (USFWS)

This week's compare and contrast is from the National Marine Life Center.