insect classification 4
Spiders: identification, venom, and safety
Overview: Spiders and related arthropods cover a broad range of forms. Although many people fear spiders, only a small fraction are problematic for health.
The number of species that are problematic for health is very low: about out of around world-wide, with only a few in the US to be particularly aware of.
Importance of correct identification to assess risk and avoid unnecessary fear.
Black Widow (Latrodectus spp.)
Identification:
Not hairy; shiny black body.
Distinctive red hourglass on the underside of the abdomen (often also seen as two small triangles pressed together).
In western US, females show the half-globose abdomen with red markings; males are much smaller and typically brown to white, with palps that are relatively large for their size.
Sexual dimorphism and mating:
Palps are the swollen structures used by males to transfer sperm (described as turkey basters).
Mating behavior involves the male sometimes tying or restraining the female briefly; the female soon releases, allowing the male to escape. This is a short-term constraint rather than a permanent hold.
Web and behavior:
Web type: cobweb spiders (family Theridiidae); not a classic orb web.
Webs have a pattern; sticky threads are laid down and touch the ground, forming a structure that, when prey hits, pulls up into the web where the spider can capture it.
Venom and effects:
Venom is a neurotoxin, affecting the nervous system.
Symptoms can include stomach upset, blurred vision, nausea, and potential breathing effects. Death is extremely rare and usually due to severe neuromuscular effects leading to respiratory failure.
Interaction with humans:
Bites are uncommon; even when bites occur, they are typically not life-threatening.
Notes: Black widows are generally not aggressive and will defend themselves if stepped on or provoked.
Brown Recluse (Loxosceles spp.; violin spider)
Identification:
Very characteristic violin-shaped marking on the cephalothorax (prosoma).
They belong to the “violin” group within the recluse-related spiders and are part of a larger set of related species in the western US.
They have six eyes arranged in three pairs, which is unusual for spiders (most have eight).
Habitat and behavior:
Webs are not the classic orb webs; recluse spiders tend to be reclusive, often occupying dark, undisturbed indoor or sheltered outdoor areas.
They may live in corners, boxes, and other secluded spaces; they do not typically build prominent webs.
Venom and effects:
Venom is proteolytic (tissue-destroying) rather than neurotoxic; it destroys tissue around the bite rather than directly affecting the nervous system.
Bites can lead to localized tissue necrosis and slow healing; secondary infections can complicate healing; untreated bites may persist for months to years.
Range and prevalence:
Historically associated with the Midwest; however, multiple related species are present in the West, including regions like New Mexico.
The commonly cited “true brown recluse” range is limited, but related species (e.g., Apache violin spider) occur more broadly in the West.
Medical and identification caveats:
Documented brown recluse bites are extremely rare; many bite-like injuries are fungal or bacterial infections or other conditions mimicking brown recluse bites or misattributions from internet lore.
Distinguishing from other look-alikes:
House spiders may resemble brown recluse, but differences include eye pattern and web behavior; the brown recluse is generally not web-building in the same way as many other spiders.
Other notes on spiders and safety
Many tarantulas and other large spiders may wander in late summer; not true migrations but males wandering to find mates.
Practical safety tip: always check shoes and clothing before wearing them; occasional wandering arachnids or other arthropods can hide in footwear or boxes.
Do not resort to extreme measures (e.g., blowtorches) to kill spiders; such actions can cause fires and injuries.
Tarantulas (myth vs. reality)
Lifespan:
Females: typically to years.
Males: usually shorter, often to years.
Mating and behavior:
Males commonly wander in search of females; this wandering can be mistaken for migration.
If kept in captivity, males tend to roam and may die earlier; females live longer and larger.
Handling and display:
If handling, ensure safety and minimize stress; avoid dangerous handling practices.
Common misconceptions:
“Migration” is not accurate for tarantulas; movement is driven by mating behavior, not a seasonal mass movement.
Real-world examples and anecdotes from the lecture
A snake-eating black widow was observed due to its strong silk, illustrating the robustness of their web and feeding habits.
The strength of black widow silk is noted as being unusually strong relative to other spider silks.
Visual identification cues (e.g., the red hourglass on the underside of the abdomen) are emphasized for quick recognition.
Summary of venom types and implications
Neurotoxin (e.g., black widows): affects the nervous system; can cause systemic symptoms, potentially leading to respiratory issues in severe cases.
Proteolytic venom (e.g., brown recluse): destroys tissue at the bite site; can result in long-lasting lesions; primarily a local tissue effect rather than systemic neurotoxicity.
Five major arthropod groups (overview; taxonomic context)
Crustacea
Aquatic and some terrestrial forms; includes crabs, lobsters, various aquatic crustaceans.
Myriapoda (centipedes and millipedes)
Centipedes (Chilopoda) typically have one pair of legs per body segment and are generally predators; millipedes (Diplopoda) have two pairs of legs per body segment and are detritivores/herbivores with a more armored body.
Diplopoda (Millipedes)
Characteristic two pairs of legs per segment; primarily detritivores.
Arachnida
Spiders, scorpions, ticks, mites; eight-legged (mostly); includes the true spiders discussed above.
Insecta
Six legs (three pairs); three body regions (head, thorax, abdomen); many have wings (though not all do).
Insects are the only major arthropod group with true wings, and wings can be two pairs in many species.
Key identification features to distinguish insects from other arthropods:
Three pairs of legs
Three body regions
One pair of antennae (insects) rather than multiple antennae in some other groups
Wings and flight:
Insects typically have wings, and those wings can be present or absent; when present, weighing the majority is that two pairs exist in many groups, with exceptions.
Practical implications:
If you’re selecting a project, you can focus on any arthropod (including spiders and other arachnids) as long as it is within Arthropoda; snails are mollusks and not appropriate for these insect-focused notes.
Insect Orders: quick reference and key features
Order Odonata — Dragonflies and Damselflies
Major groups: dragonflies (bulkier) and damselflies (delicate).
Wing position: dragonflies hold wings out to the sides when at rest; damselflies hold wings folded over the abdomen.
Ecology: predators both as adults and aquatic nymphs; nymphs live in water.
Nymph anatomy:
Damselfly nymphs have rear gills and can swim; dragonfly nymphs have a mask-like extendable mouthpart (labium) used to capture prey.
Dragonflies can also employ jet-propulsion via water movement from the rectum in aquatic life stages.
Notable note: many dragonflies and damselflies are migratory or move in large numbers at certain times.
Order Orthoptera — Grasshoppers, Crickets, Locusts, and Relatives
Common examples shown: cricket, grasshopper, Jerusalem cricket (a.k.a. Jerusalem cricket).
Sound production: crickets and related species produce sounds; mentioned as a topic to be discussed later (stridulation).
Locusts: often synonymous with migratory grasshoppers in common usage, but cicadas are not locusts; locusts are large migratory grasshoppers.
Wings: typically leathery; camouflage strategies discussed.
Diet: generally herbivores; crickets can be omnivorous and may scavenge on dead insects or plant matter; mantids are predatory (note: mantids previously grouped here but now classified separately).
Order Hemiptera — True Bugs
Suborder highlighted: Heteroptera (true bugs with half-leathery, half-membranous wings).
Wing structure: each wing has a basal leathery part and an distal membranous part; wings cross to form an X on the back when resting.
Notable examples and terms:
Cicadas (often heard calling in trees; previously miscalled locusts).
Aphids, cicadas, leafhoppers, planthoppers, whiteflies.
Water bugs and water striders (skate on water surface due to specialized foot hairs; predatory on small insect prey).
Stink bugs are true bugs (not beetles); leaf-footed bugs are true bugs with expanded legs.
Assassin bugs (predatory true bugs).
Practical notes:
The term "stink bug" can lead to confusion with beetle-like insects called stink beetles; true stink bugs are hemipterans.
Order Coleoptera — Beetles
Key feature: two pairs of wings with a hardened first pair (elytra) that shield the second pair of wings used for flight.
Appearance: a dorsal elytral shield that forms a straight line down the back; the second pair of wings unfold beneath.
Notable examples mentioned:
Tiger beetles — highly predatory and visually striking.
Blister beetles.
Dung beetles.
Rhinoceros beetles (scarab group; large beetles in the Scarabaeoidea/Scarabaeidae family).
Diversity:
Beetles are incredibly diverse; about half of all described insect species belong to Coleoptera, with estimates around described species.
Common misnomers:
Stink bugs are not beetles; true stink bugs are hemipterans.
Order Neuroptera — Lacewings, Antlions, and Relatives
Lacewings (green lacewings) are predatory and beneficial for controlling aphids.
Antlions (adult stage resembles lacewings; larvae are pit-trappers called doodlebugs).
Notable larval behavior: antlions build sandy pits and use camouflaged bodies to ambush prey; larvae use jaws to capture prey.
Doodlebug larvae have hollow mandibles and are highly predatory.
Order Lepidoptera — Butterflies and Moths
Shared feature: wings covered with scales; color and patterns due to scales that rub off on contact.
Life cycle: caterpillars (larvae) and adult moths/butterflies (adults).
Feeding: most Lepidoptera are herbivores in the larval stage; most adult moths/butterflies feed on nectar or not at all depending on species.
Notable examples: several visually striking species (e.g., the Question Mark and the Comma, which have distinctive wing shapes and metallic coloration).
Notable local example: white lion sphinx caterpillar (large sphinx moth larva) with a horn-like projection that is not a stinger but a defensive projection.
Order Hymenoptera — Bees, Wasps, Ants, and Velvet Ants
Key feature: stinging capability is present in this order; many species are beneficial pollinators or predators.
Local examples shown: bees (honeybees and bumblebees), various wasps, carpenter ants.
Velvet ants (Mutillidae): not true ants; female is wingless and extremely stinging; velvet ants are sometimes called cow killers due to painful stings.
Notable species: Thistle-down velvet ant (a visually striking wasp that resembles a fuzzy ant).
Order Diptera — Flies
Note: not deeply detailed in the lecture, but Diptera is the order containing true flies; typically characterized by a single pair of wings and halteres (stopping organs) used for balance.
Practical implications and study tips from the lecture
Understand the five major arthropod groups and one key set of distinguishing features:
Insects: 6 legs, 3 body regions, often wings (two pairs in many orders but not all).
Spiders and other arachnids: eight legs, two body segments (cephalothorax and abdomen) in spiders; includes dangerous and non-dangerous species.
For exams: be able to name the major insect orders and match them to common examples (e.g., Odonata = dragonflies/damselflies; Coleoptera = beetles; Lepidoptera = butterflies/moths).
Taxonomy note: some traditional groupings are outdated (e.g., older classifications grouped cockroaches, mantids, and walking sticks together under Orthoptera; modern taxonomy places them in separate orders).
Remember: not all insects have wings; the presence or absence of wings is variable, and wings may be present in two pairs or not at all depending on the species.
Statistical and numerical references to note for exams
Problematic spider species: approximately out of roughly species globally.
Brown recluse bites: documented bites are extremely rare; many bite-like injuries have other causes (fungal, bacterial, or different arthropods).
Tarantula lifespans: female years; male years.
Beetle diversity: about described beetle species (roughly half of all described insect species).
Ethical, philosophical, and practical implications
Taxonomic clarity matters in education and public understanding; common names (e.g., locust vs cicada) can cause confusion, underscoring the value of precise taxonomy.
Ethical handling and safety: the speaker discourages dangerous actions (e.g., using a blowtorch to kill spiders) and advocates learning to identify and avoid bites rather than sensationalized methods.
Real-world relevance: understanding arthropod diversity supports pest management, conservation, and appreciation of ecosystem services (e.g., dragonflies controlling mosquitoes; lacewings eating aphids; pollinators among Hymenoptera and Lepidoptera).
Connections to broader topics
The lecture connects arthropod diversity to foundational biology concepts: anatomy (body regions, limb counts), reproduction (mating behaviors), feeding strategies (predators vs. herbivores), and ecological roles (predation, pollination, decomposition).
It also ties into practical lab skills: identifying key morphological features, recognizing venom types and their effects, and understanding how behavior and environment influence exposure risk.
Quick reference glossary (aids for exam prep)
Neurotoxin: a venom that primarily affects the nervous system.
Proteolytic venom: a venom that destroys tissue at the bite site.
Elytra: the hardened front pair of wings in beetles that covers the flight wings.
Labium: a mouthpart in dragonfly nymphs used to capture prey (extensible “mask”).
Doodlebug: common name for antlion larva.
Velv et ant: common name for certain wasps that mimic ants and have potent stings.
Final reminder
The lecture emphasizes recognizing major arthropod groups, understanding the basic biology and ecology of representative species, and applying careful observation to distinguish similar-looking species to avoid misidentification and unnecessary fear.