Insects & Arachnids

While not as noticeable as our birds, there are many insects and arachnids living on the Hayward Shoreline who are vital members of the marsh ecosystem. Stop and look around, especially during spring and summer, and you'll find amazing small creatures all around you. Here are some of our most commonly seen insects and arachnids. 
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Anise Swallowtail
Papilio zeliacon
This stunning yellow and black butterfly lays its eggs on the Sweet Fennel which grows along Breakwater Avenue. Look for its caterpillars munching on the plants in summer and fall - the tiny ones are black and white (camouflaged as bird droppings) and the large ones are green with black and orange spots.

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Black and Yellow Mud Dauber Wasp
Sceliphron caementarium
If you visit the shoreline in summer you’re bound to see these non-aggressive insects flying around. The large ones you see are the females, who gather up mud from the marsh to build nests for their young. Once a cell in the nest has been made, the wasp will hunt for spiders and paralyze them with her sting, then carry the spider back to the nest. After filling the cell with paralyzed spiders, she will lay an egg it. When the egg hatches, the larva consume the paralyzed spiders then metamorphose into an adult, emerging from the nest in the spring. Look for their mud nests on the side of the Interpretive Center.

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European Mantis Mantis religiosa This is the original Praying Mantis and is an introduced species in North America. Voracious predators of anything they can get their raptorial forelimbs on, Praying Mantises sit in wait for prey to come close enough for them to grab. While there are other mantises in California, you can distinguish these by the dark spots in the “armpits” of their front legs.
Funnel-weaving Spiders
Family Agelenidae
Look for these spiders’ distinctive sheet-like webs on low-lying vegetation throughout the marsh. They weave a funnel from one end of the web where they lie in wait. Once it feels vibrations on the web, the spider will rush out and grab it if it's prey. These spiders are not aggressive and their venom is not medically significant to humans. They are an important part of the marsh’s ecosystem and help control insect populations.

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Non-biting Midges
Family Chironomidae
As their name suggests, these mosquito relatives do not bite - in fact, they don’t even have mouths - in their flying adult form. These numerous animals are an important part of the marsh’s food web, as their aquatic eggs, larvae (aka bloodworms) and pupae provide food for numerous birds and insects, like grebes and dragonfly larvae, and the adults are prey for swallows, spiders, and other terrestrial predators.

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Western Pygmy Blue Butterfly
Brephidium exilis When you’re out on the trail in summer and fall, look for the smallest butterfly in North America as it flutters low over the vegetation. If you stay still you’ll probably get a good look at these exquisite jewel-like insects whose upper wings are a coppery brown and underwings are blue and copper with black spots. Their wingspans are no more than ½ - ¾ of an inch!

Contact Us

  1. Hayward Shoreline Interpretive Center
    4901 Breakwater Ave.
    Hayward, CA 94545
    (510) 670-7270


    Friday - Sunday
    10:00 AM - 5:00 PM

    Closed Nov. 11 & 25