Class Arachnida

The Class arachnida is a large and diverse group.  All arachnids belong to a subphylum (a division of Arthropoda) known as the Chelicerata, of which there are approximately 65,000 described species (~8,000 in North America).  They are characterized by having two body regions, a cephalothorax and an abdomen.  They also have 6 pairs of appendages:  4 pairs of legs and 2 pairs of mouthpart appendages, the first are called chelicerae (hence, the subphylum Chelicerata).  The second pair of mouthpart appendages are called pedipalps.  Most authorities recognize 11 orders within the arachnida.  Here, we introduce you to three of them.

Order Scorpiones

Scorpions are relatively large arachnids.  Like other arachnids, their body consists of a cephalothorax, which bears the mouthparts and legs, and an abdomen.  They are characterized by having four pairs of legs, large clawlike pedipalps, and a five-segmented abdomen with a sting on the distal end.

There are about 40 species of scorpions in the United States, but only one is highly venomous and may be fatal.  The sting of most species is painful and accompanied by swelling and discoloration.  Scorpions feed primarily on other arthropods, such as insects and spiders. 


Order Araneae

The spiders are characterized by having four pairs of legs and the cephalothorax and abdomen (typically unsegmented) joined by a narrow pedicel.  The pedipalps of some spiders may appear leg-like.  Most spiders have eight simple eyes (ocelli) on the cephalothorax.

There are approximately 3,700 species of Araneae in North America and more than 38,000 worldwide.  Although nearly all spiders have venom glands, only a few species are considered dangerous, such as the black widow and the brown recluse.  The cephalothorax contains the eyes, mouthparts, legs, and stomach.  The abdomen houses the primary reproductive structures, respiratory system, intestine, silk glands, and spinnerets,  from which the silk is spun. 


Order Acari

The ticks and mites are a large group of small arachnids.  The body is typically oval with little differentiation between the cephalothorax and abdomen, which are broadly joined.  The larvae have only three pairs of legs and acquire an additional pair after the first molt.

Ticks and mites occur just about anywhere animal life is found.  They may be terrestrial or aquatic, free-living or parasitic.  Some feed on organic debris, while other live on plants or animals.  On plants, they may become serious pests while parasitic forms can be pests of man and other animals.  With over 30,000 described species of ticks and mites, this is the largest order within the class arachnida.

Entomology News at Nebraska

Breaking Entomological News...

  • Samantha DanielGraduate student Samantha Daniel did an awesome job being interviewed  by KODY radio about overwintering insects!!  Samantha is a master's student mentored by Dr. Julie Peterson.
  • Dr. John RubersonDr. Tom WeisslingCongrats to John Ruberson and Tom Weissling who were honored at the University of Nebraska-Lincoln's Family and Friends Recognition Awards. These awards are nominations by parents for faculty and staff who have a made a significant difference in the students’  lives. Tom has now been recognized twice with this award! Congratulations! And a big thank you to the thoughtful students and parents.
  • Dr. Jeff BradshawDr. Jeff Bradshaw was chosen as president-elect of the North Central Branch of the Entomology Society of America. Bradshaw is an associate professor of Entomology, extension specialist, and interim director of the Panhandle Research and Extension Center in Scottsbluff. 
  • Entomology Alumna Jennifer Weisbrod was recently selected as the new Pesticide Safety Education Program coordinator in the Department of Agronomy and Horticulture. Weisbrod graduated with her master's degree in Entomology in 2020 and is taking the reins from her predecessor Clyde Ogg, emeritus extension educator.
  • Dr. Sylvana Paula-MoraesCongratulations to departmental alumna Dr. Silvana Paula-Moraes who was recently named the recipient of the 2021 Department of Entomology Alumni Recognition Award. She presented a online seminar in connection with the award on Monday, March 1, 2021.
  • 7 seal awardThe UNL Department of Entomology has been awarded the Seven Seals Award by the Employer Support of the Guard and Reserve (ESGR). The Seven Seals Award is presented in recognition of significant individual or organizational achievement, initiative, or support that promotes and supports the ESGR mission, to include the efforts of the more than 4,500 volunteers who carry out ESGR’s mission across the nation on a daily basis. The Entomology Department is fortunate to support Courtney Brummel and Sheldon Brummel in their service to the nation. Thanks for the nomination, Courtney and Sheldon!