Find out how spiders protect their eggs and how the newly hatched spiders make their way into the world.
Spider egg sacs are a crucial part of the spider life cycle. Female spiders produce egg sacs to carry and protect their eggs until they are ready to hatch. Spider egg sacs can vary greatly in appearance but share some common characteristics. In this comprehensive guide we will cover everything you need to know about these fascinating structures.
What Is a Spider Egg Sac?
A spider egg sac is a silk structure spun by a female spider to contain and protect her eggs. The eggs are fertilized by the male spider before being deposited into the sac.
The silk casing allows gas exchange to occur but protects the eggs from desiccation, predation, and environmental hazards Spider egg sacs come in a variety of shapes, sizes, and textures depending on the species
Why Do Spiders Make Egg Sacs?
Female spiders make egg sacs for the following key reasons
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To protect the eggs: The silk casing shields the vulnerable eggs from threats like predators, parasites, and weather. Some sacs even have extra camouflage features.
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To retain moisture: The sac prevents the eggs from drying out before hatching. Some spiders add a waterproof outer layer.
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For gas exchange: While protective, the sac allows oxygen and carbon dioxide to permeate so the embryos can develop.
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To contain the eggs: The sac keeps the eggs neatly in one place for the female to carry or guard.
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For temperature regulation: Silk is an excellent insulator that helps regulate temperature inside the sac. Some spiders anchor sacs in sunny or shady spots to control this.
What Do Spider Egg Sacs Look Like?
Spider egg sacs vary in appearance depending on the species. Some distinctive features to look for include:
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Shape: Spherical, tear-drop, disk-shaped or irregularly shaped.
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Size: From tiny 5mm sacs to large 50mm sacs. They are rarely bigger than the spider itself.
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Texture: Smooth, soft, papery, silky, wooly, or with spiky protrusions.
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Color: White, yellow, brown, or greenish. Never brightly colored reds/pinks.
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Markings: Some have camouflage features like dirt, debris, or zig-zag ‘stitching’.
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Location: Attached to webs, hidden in retreats, anchored to surfaces, or carried by the spider.
How Are Spider Egg Sacs Made?
Spider egg sac construction is a complex process. Here are the basic steps:
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The female spider fertilizes the eggs internally via the male’s pedipalps.
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She produces liquid silk in her abdomen and spins this into threads.
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With her legs and spinnerets, she weaves the threads into the sac shape.
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Next, she deposits the eggs inside the sac, using her legs and ovipositor.
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Finally, she seals the sac and attaches protective outer layers if needed.
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The female will either anchor the sac in place or carry it until the eggs hatch.
How Many Eggs Are Inside a Spider Egg Sac?
The number of eggs inside a spider egg sac can range dramatically by species. Some examples:
- Black widow sacs contain 100 – 400 eggs.
- Fishing spider sacs have up to 1,000 eggs.
- Garden spider sacs average 400 – 1,000 eggs.
- Recluse spider sacs hold 50 – 100 eggs.
- Wolf spider sacs have around 100 eggs.
- Jumping spider sacs can have 20 – 30 eggs.
Bigger spiders tend to produce more eggs per sac, maximizing their reproductive success.
What Happens Inside a Spider Egg Sac?
A lot happens inside a spider egg sac to change the eggs into baby spiderlings! Here are the developmental stages:
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Fertilization: The egg is fertilized internally by the male’s sperm before being laid.
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Cleavage: The fertilized egg divides into 2, then 4, then 8 cells, and so on.
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Blastula stage: A hollow sphere of cells forms.
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Gastrulation: A gastrula forms, with embryonic tissue layers.
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Organogenesis: Body segments and organs begin developing.
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Hatching: The spiderling breaks out of the egg casing and sac.
The whole embryonic process takes several weeks to months depending on the species. The babies emerge looking like tiny versions of the adults.
What Do Newly Hatched Spiderlings Do?
Spiderling behavior right after hatching depends on the species. Here are some common behaviors:
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Stay inside the egg sac for their first molt.
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Climb onto the mother’s abdomen and ride around for safety.
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Scatter away from the egg sac immediately to avoid cannibalism.
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Remain together near the sac for days or weeks.
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Build tiny webs close to the mother’s web.
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Receive food from the mother in her web or burrow.
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Hunt prey independently if the mother abandons the sac early.
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Cannibalize unhatched eggs or weaker siblings.
Are Spider Egg Sacs Dangerous?
Spider egg sacs are rarely dangerous. While some contain venomous spiderlings, the babies usually leave immediately or lack ability to bite humans.
Gently removing and properly disposing of sacs is recommended. Never intentionally break or squash sacs as the spreading spiderlings are inconvenient. Monitor vacuumed sacs closely in case they rupture.
Bites or allergies from emerging spiderlings are unlikely but possible with highly venomous species like widows or recluses. Seek medical attention if bitten.
What Should I Do If I Find a Spider Egg Sac?
If an egg sac appears in or near your home, you have a few options:
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Leave it alone if the species is harmless. Many garden spiders or cobweb spiders are beneficial pest controllers.
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Vacuum up the sac carefully and seal it before disposal if you don’t want spiderlings spreading.
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Place the vacuumed sac in a jar and check if spiderlings emerge. Release them outside.
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Remove and relocate the sac outside if the weather is appropriate.
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Search for more sacs which may indicate an infestation of unwanted spiders inside.
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Identify if the sac belongs to a dangerous spider species like widows or recluses. Seek professional pest control in this case.
Never intentionally destroy or handle dangerous spider egg sacs without proper precautions.
Can Spider Egg Sacs Be Prevented?
It is difficult to fully prevent spider sacs from appearing inside or outside the home. But you can reduce the likelihood:
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Install screens on windows and doors to block spiders entering.
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Seal cracks and crevices where spiders access buildings.
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Remove clutter piles where spiders hide and build sacs.
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Keep the property free of dust and insect infestations.
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Vacuum and clean garages and basements regularly.
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Remove spider webs promptly before they are used for sacs.
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Use pest control sprays, but research impact on beneficial spiders first.
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Introduce natural spider predators like lizards or birds in your yard.
Fascinating Facts About Spider Egg Sacs
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Some female spiders die shortly after making their final egg sac, devoting all their energy and resources into maximizing reproductive success.
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Certain spiders produce multiple egg sacs from one mating while others produce just one. Some make up to 9 sacs!
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A few spider species care for the spiderlings after hatching by sharing their web or bringing them food. Most abandon the sac.
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Spider egg sac parasitism is common. Sneaky wasps, flies, and other spiders will inject their own eggs into sacs.
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Spiderlings often hatch all at once, emerging from the sac within hours. Others hatch gradually over weeks.
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Not all eggs are fertilized or survive, so sacs often contain both spiderlings and undeveloped eggs.
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Some clever spiders disguise their sacs with objects like shells, seeds, plant matter or prey remains for camouflage.
Spider egg sacs are intricate, masterfully crafted structures that play an essential role in spider reproduction. While their appearance and locations vary among species, the silken casings all serve to protect the next generation until hatching. Studying egg sacs can reveal a lot about spider diversity in an area. With care and relocation, even unwanted spider sacs in your home can be addressed safely.
Egg sacs and maternal care
The egg sac silk protects the eggs against physical damage and excessive drying, wetting or heating, as well as providing a shield against predators like ants and birds. However, this protection is often breached by parasitic wasps, flies and mantispid lacewings that succeed in laying their eggs or infiltrating their larvae among or within the spiders eggs. Spiders like redbacks lay many eggs and make several egg sacs to ensure that enough eggs survive these seasonal onslaughts.
The eggs of many spiders are glutinous and stick together allowing them to be laid in a continuous stream into the partly built silk egg sac. They vary in colour from pearly white to green and in number from 4 to 600 in a single egg sac, depending on the species concerned.
Egg sacs come in all shapes, sizes and colours. They may be built inside a burrow (e.g, trapdoor spiders), under bark (e.g, huntsman spiders), in the web (e.g., black house spiders), in a curled leaf (e.g., leaf curling spiders), suspended on a long line (two-tailed spiders), or hidden among foliage (e,g., orb weaving spiders). Some spiders stay with the egg sac, guarding it until the spiderlings emerge (e.g, huntsman spiders, trapdoor spiders) or carry the egg sac about with them (wolf spiders, water spiders), sometimes in their jaws (daddy-long-legs spiders). Wolf Spiders carry their spherical egg sacs slung from the spinnerets. When the young hatch they climb onto the mothers back, clinging to special knob-shaped hairs. The mother carries them about until they moult and disperse.
In many species, like orb weaving spiders, the egg sacs are simply abandoned, sometimes protected among leaves or in silk barriers, or even shallowly buried in soil (Nephila pilipes). Exposed egg sacs usually have a surface silk layer of dull brown, green or russet coloured silk, often further camouflaged with leaf debris to help prevent eggs being eaten or parasitised.
After hatching from the eggs the spiderlings stay within the egg sac until they undergo their first moult – their small cast skins can be seen inside the old egg sac. After this they emerge, having cut a neat hole in the sac with the fangs (perhaps aided by a silk digesting fluid and sometimes helped by the female from outside). The spiderlings cluster together initially, still living largely upon the remnants of yolk sac in their abdomens.
After several days (or weeks in the case of some mygalomorph spiders) and sometimes another moult, the spiderlings begin to disperse gradually away. This is necessary to avoid competition for food and prevent cannibalism among the hungry siblings. Some species, especially ground and burrow dwellers, disperse by walking, often over only relatively short distances. Others, especially foliage dwellers and many web builders, but also wolf and mouse spiders, disperse by bridging and ballooning. Bridging is a means of travelling by repeated climbing up through foliage and then dropping down on a silk line to cross to adjacent branches, often with some breeze-assisted swinging. Ballooning involves ascending to a high point on foliage and letting out fine silk lines that catch the breeze and eventually gain enough lift to waft the spider up and away. While long distance flights can occur (Charles Darwin noted spiderlings landing on the rigging of the Beagle, 100 km out at sea), the more usual outcome is for spiders to be deposited anything from a few metres to a few kilometres from the start point.
Simultaneous ballooning by thousands of spiderlings can result in a remarkable carpet of silk, called gossamer, covering shrubs or fields.
Having survived the perils of wasp, fly and mantispid lacewing egg parasitism in the egg sac, the life of spiderlings remains beset with dangers. Only a few will avoid being eaten and find adequate shelter and food to ensure their survival to adulthood, so any help is useful. The first orb webs of St Andrews Cross spiderlings have a doily-like patch of white silk at the centre which may be both attractive to insect prey and provide a hide for the spider to disappear behind when predators appear. Some spiderlings simply dont leave home and grow up in communal webs and dispersing just before maturing (e.g., Phryganoporus candidus). Sticky web building spiderlings can partly support themselves simply by eating their own webs. Sticky webs like orb webs pick up valuable nutrients such as pollen grains that simply get windblown onto them – and, because sticky silk absorbs moisture from the air, which also condenses as dew on silk lines, the spiderling gets a drink as well.
4 Deadly Spider Egg Sacs Whats Inside Is Amazing
FAQ
What to do if you find a spider egg sac?
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Vacuuming:Use a vacuum cleaner with a hose attachment to suck up the egg sac.
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Disposal:Immediately dispose of the vacuum bag or empty the canister outside to prevent any spiderlings from escaping.
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Alternatives:If you don’t have a vacuum, you can use a broom to sweep up the egg sac and dispose of it in a trash bag.
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Caution:Be careful when handling the egg sac, as disturbing it might release spiderlings.
Should I destroy spider egg sac?
Don’t worry about destroying her web, the spider can always make a new one if she continues to stay in the area. You can simply dispose of the eggs, take them outdoors, or place them in a jar if you want to see if they will hatch.
What does a spider egg sac look like?
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Shape and Size:They can be round, oval, or even teardrop-shaped, and their size varies greatly depending on the spider species, ranging from small marbles to pea-sized.
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Color:Spider egg sacs can be white, cream, pale yellow, brown, or even green, depending on the spider species and environmental conditions.
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Texture:The texture can range from smooth and sleek to fuzzy or even spiked, depending on the density and arrangement of the silk threads.
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Location:Egg sacs are often found in corners, under furniture, in webs, or even attached to leaves or other objects.
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Some spiders, like wolf spiders and fishing spiders, carry the egg sac with them, while others create a silken tent or nest to protect the eggs.
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Examples of egg sacs:
- Black widow: Black widow egg sacs are robust, often spherical, and have a papery texture.
- Wolf spider: Wolf spiders carry their egg sacs attached to their spinnerets.
- Brown recluse: Brown recluse spiders create loose, off-white sacs.
- Black widow: Black widow egg sacs are robust, often spherical, and have a papery texture.
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Identifying spider egg sacs:
- Check corners, cluttered areas, and under furniture.
- Look for small, round or oval-shaped silk structures.
- Consider the size, shape, color, and texture of the sac.
- If you see a sphere that is much larger than a quarter, it is unlikely to be a spider egg sac.
- Check corners, cluttered areas, and under furniture.
How many babies are in a spider egg sac?