Garden Friends—keep ‘em, don’t kill ‘em

by Norm Budnitz

Squash that bug.  Stomp that spider.  Squish that worm. 

Well, sometimes ‘yes,’ sometimes ‘no,’ and sometimes ‘maybe.’ 

Many true bugs (stink bugs, squash bug, harlequin bugs, etc.) are bad guys in the garden.  They stick their piercing mouth parts into a plant and suck out its juices.  ‘Yum’ for the bug; ‘grr’ for the gardener.  An infestation of squash bugs can leave your butternuts looking like limp lumps.  But there are some good guy bugs—predatory bugs.  These insects attack other insects, often harmful ones. 

Most spiders are good guys (mostly gals, actually) in the garden.  These arachnids (not insects) spend their lives eating lots of the bad guys.  So don’t kill spiders, just wiggle their webs a little and they will move out of the way and hide for a while.  It’s true that when humans get bitten by spiders they may be in for a bit of pain or sickness or even death in rare cases (the proverbial black widows and brown recluses).  But most spiders, including those two dangerous ones, would much rather scurry out of the way when a big old mammal wanders by. 

The common garden spider (Argiope aurantia) is a big beautiful female who often sets up shop in or on the edge of the garden.  Her web is quite a large affair—a circular orb, 1 to 2 feet in diameter, suspended by strong, straight strands of silk that can be 5 feet long or more.  She is striking with her black and yellow abdomen about the size of your thumb.  And she reinforces her web with bright, thick strands of silk that she lays down in a zigzag pattern that sometimes seems to spell out things (MMMM in the picture here).  The male garden spider is a thin, lanky little brown guy who builds a smaller web.  His sole job is to eat enough to get the energy to breed with a female, after which he dies, sometimes being eaten by his mate.

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Tobacco hornworms, Manduca sexta (pictured here feeding on a pepper plant), and tomato hornworms, Manduca quinquemaculata, are big green caterpillars—not worms in the sense of earthworms.  They have white slashes along their bodies, a horn on the tip of their butt, and can get up to 3-4 inches long.  Hornworms feed on members of the nightshade family—tomatoes, peppers, eggplants, tobacco, and potatoes.  In spite of their names, both of these species will happily eat any of these crops.  They are quite impressive beasts and can eat a lot of foliage in a short period of time.  Bad guys in the garden!

Here’s the good guy (gal, again)—a wasp called a braconid.  When the female braconid is ready to lay her eggs, she goes in search of a hornworm.  She has a long ovipositor (egg depositor) sticking out of her abdomen that she sticks into the caterpillar.  The eggs are laid inside the hornworm where they hatch into larvae and grow, eating the caterpillar from the inside.  The hornworm stops eating and eventually dies.  After the larvae have had their fill, they turn into pupae and build a cocoon around themselves when they emerge from the hornworm.  In the picture here, the hornworm has lots of little rice grain sized cocoons sticking to it.  Eventually, each one of these pupae will undergo metamorphosis like a butterfly.  But instead of a big, beautiful butterfly, it will become a wasp—beautiful in its own right—that will go on to parasitize another hornworm someday.

As for the hornworm, it’s not all bad either.  True, it’s a bad guy when it’s eating a lot of tomato leaves.  But if it pupates successfully and undergoes metamorphosis, it will emerge as a sphinx moth or hawk moth, sometimes even called a hummingbird moth.  Its job in the garden is to pollinate flowers while it gathers nectar.  No pollination, no fruit.  So the larvae may eat the leaves, but the adults help to make the tomatoes.

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