I know what you’re thinking: this is an insect spotlight, but you are writing about spiders! They are not insects! Well, you are correct. They are not insects but rather Arachnids. However, they are closely related, studied by Entomologists, and play an important role in arthropod food webs, so bear with us. Hopefully, this article will help you appreciate this ‘scary’ critter.
The order Aranea (spiders) is extremely diverse. Most species prefer tropical climates, but they can be found all over the world and are important in agricultural systems. Similar to insects, spiders have exoskeletons (bones on the outside). Differences in anatomy from insects include that spiders only have two body parts (as opposed to the three insects have): a cephalothorax and an abdomen. While insects have six legs, spiders have eight! Spiders do not have antennae. They can only eat liquid and, therefore, use digestive enzymes to break down their food and chelicera (like teeth) to grind food. They are very interesting creatures!
Leaving aside the fear that many people have, spiders are one of the best generalist predators in nature; among the diversity, you can find a wide variety of behaviors that have evolved to capture prey, which includes many agricultural pests. Some of these behaviors are used to organize or classify different types of spiders. For example, the family Araneidae (Fig. 1, orb-weaver spiders) build their webs in a spiral wheel shape, which is useful for catching flying insects. One of the most studied species is the Cyrtophora citricola, which builds bigger and stronger webs than most and has been studied to control caterpillars and moths in tomato production systems.
Figure 1. Orb-weaver (Araneidae) spider preying on a squash bug (Photo by John Obermeyer).
Figure 2. Wolf Spider (Lycosidae) preying a caterpillar (Photo by John Obermeyer).
Not all spiders use webs to capture their prey. There are some that prefer to move across the ground and actively hunt their food, like the families Gnaphosidae (ground spider) and Lycosidae (Fig. 2, wolf spiders). In agricultural systems, we can promote the presence of this spider by providing ground cover or perennial borders for them to nest in and rest when they are not hunting. Many are nocturnal. A third type of spider is the sit-and-wait or ambush spider. This includes the families Salticidae (Fig. 3, jumping spiders), Thomisidae (Fig. 4, crab spiders), and Oxyopidae (lynx spider). They are more common in horticultural or fruit crops and can consume common pests such as aphids, leafhoppers, caterpillars, beetles, etc. Sometimes, they can even sit in flowers and capture various pollinators and other floral visitors.
Figure 3. Jumping Spider (Salticidae) preying a Mayfly Wood (Photo by John Obermeyer).
Figure 4. Crab spider (Thomisidae) preying on a scarab beetle (Photo by John Obermeyer).
In general, spiders play a role in biocontrol, so they should be a welcome addition to the garden. However, in Indiana, very few species can cause harm, and in almost all situations, they will retreat if they encounter a human. The downside is that you may walk into a web and disrupt their work!
Even though there are no commercially available spiders, there are things you can do to promote their presence around the farm. Reducing tillage, providing ground cover, and mulching can provide a habitat for ground-hunting spiders. Structural complexity and vertical height within the crops themselves provide habitat for the sit-and-wait or ambush spiders. After reading this article, we hope you may be a bit more friendly to spiders!