Posts Tagged ‘legs’

Aug
30

Venomous Spiders in Texas

Posted by in Insects

Spiders are an incredibly diverse and fascinating group of animals.  As with other venomous creatures, many people tend to be overly concerned about them.  Only two of the 900 species in Texas are truly dangerous and both of them are quite shy and retiring.  Bites do occur but they are rare and usually the result of accidental contact. 

Except for one taxonomic family, all spiders possess venom glands.  By far, the majority of spiders are not dangerous to people although allergic reactions can occur as with wasp or bee stings.  The only spiders of medical significance in Texas are the Black widow (Latrodectus mactans) and the Brown recluse (Loxosceles recluse).  

George the Brown Recluse

The name Black widow is actually a misnomer as the action implied rarely occurs.  Black widows have a potent neurotoxic venom which can be quite dangerous to debilitated persons and young children.  An antivenom is available for Black widow bites if deemed necessary.  Brown recluse venom is a necrotoxin which can cause tissue damage. 

Southern Black Widow

After a male’s last molt he is sexually mature and will spend the rest of his life seeking mates, oblivious to everything else including food.  Most male spiders only live for a few months after their maturing molts.  The male constructs a special sperm web onto which he deposits sperm from his genital opening.  The sperm is then taken up into the pedipalps to be later placed in the genital opening of the female.  After a few weeks the female will construct a silken cocoon in which to lay her eggs which can number from a few to several thousand.

Many spiders guard their egg cases.  Some spiders even exhibit parental care.  A wolf spider female will open the egg sac and allow the spiderlings to ride on her back for a few weeks.  There is even a spider that will regurgitate food for her offspring.

Baby Wolf Spiders on the Bus

We come close to many more spiders than we will ever know because of their size and habits.  These seemingly primitive mechanical creatures actually prove very interesting if one spends a little time observing them.

Jumping Spider - Hentzia mitrata

Written by Judith Bryja, Houston Zoo Herpetology Supervisor

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Aug
23

More than Just 8 Legs – Spiders 101

Posted by in Insects

Jumping spiderMaybe you think they’re creepy crawly or maybe you think they’re fascinating creatures. Regardless of which, spiders live with us, though not often apparent. It can help us appreciate them and be less afraid if we know more about them. And if there are ones to have a healthy respect for, educating ourselves on which those are is a good plan.

A  few quick facts to start:

  • Approximately 41,000 species of spiders have been described thus far.
  • About 900 call Texas home.
  • Spiders are placed in the Class Arachnida which also includes scorpions, mites, ticks, and seven other taxonomic orders. 
  • The lifespan of a spider can vary from a few months up to twenty-five years for female tarantulas! 
  • All spiders are strictly carnivorous. 
  • Most spiders are solitary although a few live communally and cooperate in obtaining prey.

Spiders possess two main body parts: the prosoma (front part or cephalothorax) and the opisthosoma (rear part or abdomen).  Four pairs of walking legs are attached to the prosoma.  A pair of pedipalps are in front of the first pair of legs.  These leglike appendages are used for manipulating prey. 

In the male spider, the pedipalps are used as an intromittent sex organ.  In front of the pedipalps are the chelicerae which are used for defense, subduing prey, and grasping things.  The fangs are housed in a special groove in the chelicerae. 

jumping spider

Although most spiders have eight eyes, some have only two, four, or six.

Some cave dwelling spiders have lost their eyes completely.  Most spiders have fairly poor vision; however, some can see quite well.  Jumping spiders, which actively stalk their prey, have excellent vision.  They also take the award for cutest spider as they will turn their furry heads to peer intently at you.  Spiders breathe by way of tubular tracheae and book lungs.  Book lungs (which resemble the pages of a book) are located on the ventral side of the opisthosoma and allow for air exchange. 

Spiders must molt in order to grow.  The old cuticle separates from the new and about a week later the old skin is shed.  Spiders are extremely vulnerable right after molting and until the new cuticle hardens.

a stitch in time
Silk is produced in glands at the rear of the abdomen.  The glands end in spigots at the end of three pairs of spinnerets.  Spider silk is incredibly strong.  It is used for snares as well as draglines and egg cases.  Female spiders have a special gland specifically for producing egg sac silk.  The spiral orb web is the most well known type of web.  One of our most eye catching natives, the yellow garden spider (Argiope aurantia), can be seen resting in an orb web with a zigzag in the center.

Written by Judith Bryja, Houston Zoo Herpetology Supervisor

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