FLORA and FAUNA

Spiders of Deerfield Island

Spiders are some of the most evolutionarily successful arthropods on the planet and Deerfield Island Park is home to many of them. Spiders are believed to have evolved into their present form some 380 million years ago during the Devonian Period. Unlike insects, spiders do not have antennae and share a body plan consisting of an abdomen and a fused head and thorax called the cephalothorax (prosoma). Additionally, they have twelve appendages: eight walking legs, two pedipalps which are used for feeding, and two chelicerae which contain fangs that inject venom into prey. Most spiders are highly predatory and usually prey primarily on insects or other spiders. Some species prey on larger game such as lizards and birds. Before feeding, spiders must liquify their prey’s tissues by injecting them with paralyzing venom because their gut is too narrow to process solid food. They usually leave their meal as an empty husk when done feeding.

 

Spiders are incredibly diverse and have evolved to overcome numerous challenges presented to them in their native environments. Among their most well-known adaptations is their ability to spin webs. Spider webs are made of a protein based thread called silk which weight-for-weight, has a tensile strength five times that of steel. Spiders build webs for different purposes such as trapping prey, protecting eggs, and even as a means of travel. Ballooning spiders will perch at a high point, release a long line of silk, and let the wind catch their web which can carry them hundreds of miles. Contrary to popular belief, not all parts of a spider orb web are sticky to capture passing insects. Only some areas of the web have an adhesive silk and a spider must be mindful of these areas to avoid being caught in its own trap!

 

                                    

One of the most recognizable spiders in South Florida that dwells at Deerfield Island Park is the spinybacked orbweaver. Its scientific name is Gasteracantha cancriformis which translates roughly to belly thorn and crab-shaped. It is unsurprising that this species is frequently referred to wrongly as a “crab spider.” Their most noticeable feature is their large white abdomen with black spots and six red spines that are believed to be a defense mechanism against predators. These spiders build large orb webs with small tufts throughout that are hypothesized to be conspicuous to birds to prevent any accidental collisions that would destroy the web. This web-building strategy is also effective for avoiding humans… some of the time. They also commonly build their webs near residences and especially on outdoor patios. Many people consider them a nuisance; however, these spiders are docile and keep mosquito and other pest populations in check. Their bite and venom are not known to cause any adverse health effects on humans.

Another resident of Deerfield Island Park is the golden orbweaver or golden silk spider (Nephila clavipes). This spider has a golden-brown coloration with white spots on its abdomen and long brown legs with black tufts. Being one of the largest and most noticeable on the island, this spider is certainly one of the most intimidating and is usually seen sitting motionless on its large orb web. They tend to build their webs between trees or low bushes where insect flight paths are most likely to collide with them. In the right sunlight, their webs glow a brilliant golden color, hence their name. These spiders feed primarily on flying insects such as bees, wasps, and butterflies. They have even been observed feeding on dragonflies. Like many spiders, the female is the larger and more colorful specimen and are most likely to be seen. Male golden orbweavers are a much more inconspicuous brown color, smaller in size (6mm in length), and can sometimes be found seated on the female’s web. To many, this spider can be quite frightening because of its size and color, however it’s quite harmless and will only bite if grabbed or pinched. Its bite and venom are trivial to humans and will only leave a localized red bump for a few hours.

 

A tougher-to-find but equally striking arachnid found at Deerfield Island Park is the green lynx spider (Peucetia viridans). It is a larger spider with a bright green complexion and long legs. Its legs have numerous black thorns protruding from them and small scattered black dots. Judging from its lifestyle and behavior, it is no secret its bright green complexion functions perfectly for camouflage among the shrubs and vegetation in which it dwells. This spider is highly predatory and it is considered a major consumer of insects that dwell in low shrubby vegetation. It has excellent eyesight that enables it to spot prey among the dense foliage. It jumps from plant to plant with a silk safety line attached to an anchor point as a precaution and maneuvers through vegetation with speed and ease to ambush prey. Because of its predatory behavior, this spider is considered a potential agricultural pest management option. It may be used in the future to keep crops safe from insect pests. This spider is no danger to humans and its bite is of no real concern.

Contributed by Erick Espana, Naturalist Broward County Parks

References

https://australianmuseum.net.au/spider-origins

https://baynature.org/article/spiders/

http://bugeric.blogspot.com/2014/02/spinybacked-orbweaver.html

http://entnemdept.ufl.edu/creatures/beneficial/g_cancriformis.htm

http://entnemdept.ufl.edu/creatures/misc/golden_silk_spider.htm