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Beneficial Insects In The Landscape

Posted by Darlene Caviness

Praying Mantis

Scary, Beneficial Insects

If you work within the green industry, the phrase “beneficial insects” usually brings an image to mind.  Ladybugs, Green Lacewings, predatory mites and predatory wasps are just a few beneficial insects, which are effective and available for purchase and release.  Another thing these insects have in common is that they are relatively small and innocuous looking.

 There is a whole other category of beneficials that I like to term “scary beneficials.”  Not scary in the sense that it makes you run away screaming, but large and sometimes quite startling in appearance.  Some of these insectoid behemoths have even inspired horror films.

Praying Mantis:

One of the most recognizable of the scary beneficials is the Praying Mantis.  With its characteristic posture, triangular head and large, compound eyes, a Praying Mantis is unmistakable.  Its lightning fast reflexes and extremely long grasping legs allow it to capture a variety of prey.  Insects, amphibians, mice, small birds and even other mantises are on the menu.  Mantises have been know to catch and eat prey three times its size – and the largest Mantises can grow to 4 or 5 inches in length!  However, in order to catch its prey, the mantis must get close to it.  That is where its coloring and stealthy behavior comes into play.  These sneaky insects crawl slowly into flowers, along stems, among leaves, anywhere they expect prey to be.  They are also the only insects able to swivel their heads to look over their shoulder.  I think that ability imbues them with a very alien quality.

 mantis & milkweedPraying Mantises over-winter as eggs protected in an egg case called an “ootheca.”  These cases are often seen attached to deciduous trees in winter.  In the spring, tiny nymphs emerge and begin catching prey immediately – sometimes that prey is their fellow hatchlings.  Their life cycle involves incomplete metamorphosis so the juveniles closely resemble adults.  Mantises molt several times before reaching maturity.  And yes, it is true that females will sometimes eat the male during mating.  Researchers have many theories as to why, but it is a myth that the male’s head has to be ripped off to initiate fertilization.  After mating, the female will lay approximately 200 eggs into a foamy substance secreted by glands in her abdomen.  This frothy substance will harden into the ootheca. 

 Gardeners can purchase Praying mantis egg cases and distribute them as part of their biocontrol practice.  This segment on Praying Mantises from Animal Planet contains more information and great video:

 http://www.youtube.com/watch?v=6hGuallLPcM

Wheel Bug:

Wheel Bugs are less well known than the Praying Mantis, but no less scary looking.  A memberWheel Bug of the Hemiptera or “true bug” order of insects, Wheel Bugs can reach 1.5 inches in length – a true giant of its kind.  Camouflaged in shades of gray and brown, one of the primary identifiers for this insect is the gear-shaped armor on its back for which it is named.  Its head seems ridiculously out of proportion to its body, being relatively small and shaped like the end of a billy club with a beak folded under.  However, that beak is no laughing matter.  The Wheel Bug catches its prey then pierces it with the beak and injects enzymes to liquefy the prey’s insides, which are then sucked out.  They can also use their beak to deliver a painful bite to people if necessary.  Wheel Bugs also engage in chemical warfare when threatened.  A pair of scent glands near the anus release a stench when the insect is disturbed.  While not as powerful as a stinkbug, the odor is strong enough to drive away predators and be noticed by humans.

 The female will lay a group of anywhere from 40 to 200 barrel-shaped eggs in the autumn.  When spring arrives, red Wheel Bug nymphs hatch.  These nymphs are voracious, eating aphids, caterpillars and each other.  The nymphs will molt five times before reaching maturity. 

 As scary as they may seem, Wheel Bugs eat many harmful insects.  This makes them a true beneficial.  Following is a link to a very informative video by Jeff Ore:

 http://www.youtube.com/watch?v=UnaC4iGES5E

 Spiders:

Garden SpiderThe next scary beneficials I plan to discuss are the spiders. Let’s face it; spiders can be very scary even if they are our friends.   Obviously, there are many different species of spiders that prey upon all kinds of insects, so I will discuss them in very general terms.

 First of all, spiders are not insects.  They are arachnids, belonging in the same classification as mites.  Second, spiders are carnivorous.  Third, spiders all have the ability to produce silk although different species use it in different ways.

 The most noticeable are the web spinners.  Spiders such as the Garden and Orb spiders use their silk to construct beautiful webs that are actually traps for unwary insects.  Once a victim touches the sticky web, the spider is alerted by the vibrations and quickly arrives to secure its struggling meal in additional silk.  The spider is then free to dine at its leisure.  While some web spinners produce intricately structured webs, others (such as the Funnel-Web spiders) produce webs that look messier to humans, but perform the same function.  Insects land on the web and get stuck.  Their struggling alerts the spider, which soon wraps them up, ready for dinner.

 Another group of spiders does not use webbing to trap victims; they actively hunt theirJumping Spider prey.  These spiders do produce silk - they just use it differently.  For example, Jumping Spiders use their silk as a lifeline in case they miss their prey.  They may also spin a “pup tent” as protection from the weather or as sleeping quarters. Wolf spiders wrap their eggs in a silken egg case and carry it around with them until the eggs hatch.  Surprisingly, Wolf spider females also are good mothers.  After the eggs have hatched, she will carry her young on her back.

These hunting spiders look very different from other spiders in that they have 4 pairs of eyes.  One pair is quite large and located in the center front of the head, giving them a “face.”  These predators have extremely well developed vision, allowing them to track prey.  Some species even specialize in capturing web-spinning spiders.  The stalking and hunting complexities of these is the subject of much research among scientists.Wolf Spider

 Remember – Praying Mantises, Wheel Bugs and spiders may seem scary, but they are valuable assets to the gardener, aiding in the control of plant pests.  And truthfully – they are just really cool!

 

Tags: General, Pests/Disease, Environmentally Friendly