CIrcle of Mandibles

These Druids can take the form of all sorts of arachnids- including some other orders of creatures.  Giant Scorpion, Spraying Scorpion, Tailless whip scorpion, Camel Spider, Giant spider, Giant wolf spider,  Giant Orb Weaver, Normal sized Coconut crab, Spider crab, Giant huntsman spider (for difficult terrain). 

UP TO DM WHETHER OR NOT YOU SEE THESE CREATURES. DON'T GET MAD IF YOU CANNOT USE GIBBERISH LIKE WILDSHAPING INTO A GIANT SCORPION OR CAMEL SPIDER WHEN YOUR PARTY HAS NOT LEFT THE JUNGLE. JUST HINT THAT THERE COULD BE A DESERT PART AND GROVEL FOR THERE TO BE CREATURES THERE 

Arachnid Form

At 2nd level, you can assume a more frightening form as eight large spider legs grow from your back, and webs weave the air around you to protect you. As an action, you can expend a use of your Wild Shape feature to form these threads, rather than transforming into a beast form, and you gain 4 temporary hit points for each level you have in this class. While this feature is active, you gain the following benefits:

• You gain the effects of a spider climb spell that lasts until your form ends.
• You can strike with your spider arms as a bonus action. Make a melee spell attack against a creature within 10 feet. On hit, you deal 1d6 + Wisdom modifier piercing damage, and the creature becomes grappled by two of your spider arms, provided it is no more than one size larger than you. The creature can attempt to escape this grapple by using its action to make a Strength (Athletics) check against your spell save DC, freeing itself on success.

These benefits last for 10 minutes, or until you drop to 0 hit points, die, or fall unconscious.

Arachno-Shapes

At 3rd level, You can choose to use wild shapes- but only if they count as arthropods. No other shapes. No exceptions. 

Silk Weaver

 Your time spent weaving with magic has taught you how to weave with tools. At 2nd level, you gain proficiency with weaver's tools. If you are using spider silk to weave, you add twice your proficiency bonus to the check.

Weaver Magic

 

Your harmony with spiders grants you certain magic, allowing you to better embody your venomous origin. At 2nd level, you learn the poison spray cantrip. When you cast this cantrip, a creature that succeeds its saving throw still takes half as much damage instead of none.

At 3rd level, you have the web spell prepared. It counts as a druid spell for you, and don't count against the number of spells you can have prepared.

You can cast web without expending a spell slot. You can do so a number of times equal to your Wisdom modifier, and you regain all expended uses when you finish a long rest.

Venom Strikes

At 6th level, your affinity to your arachnid kin becomes more powerful. While you are in your Arachnid Form, weapon attacks and strikes made with your spider arms deal 1d6 additional poison damage.

Additionally, while in your Arachnid Form, you treat immunity to poison damage as resistance, and your strikes with your spider legs count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.

Full Form

At 10th level, when you assume your Arachnid Form, you can instead expend two uses of Wild Shape at the same time to transform into a Weave Spider as well. The stat block for the spider is detailed at the end of this subclass.

 

or 
 use one slot of wild shape to use less powerful spider forms 

Master Weaver

At 14th level, you can pull on the strings of the weave of magic as though they were part of your web. If a creature you can sense moves within 30 feet of yourself, you can use your reaction to pull a thread of the weave taut, forcing it to make a Dexterity saving throw against your spell save DC. On failure, the creature takes 2d6 slashing damage and becomes restrained by arcane threads until the end of your next turn. On success, a creature takes half as much damage and isn't restrained. While in your arachnid form, the range of this feature becomes 60 feet, and you are aware of the exact position of any creature within that radius.

You can use this feature a number of times equal to your Wisdom modifier (minimum of once), and you regain all expended uses of it when you finish a long rest.