The locations of the ornaments in First contact goes as follows
On top of the piano

Next to the tree on the TV stand

On the Fireplace behind the photo

On the bottom shelf behind the (American)football in the closet

In the sink of the bathroom

In the tub of the bathroom

The locations of the ornaments in Close Encounters goes as follows
On the shelf behind the photo

In the bottom left drawer of the masters bedroom
Next to the toilet in the bathroom

Behind the clothes basket in the “gamer’s/teen’s” bedroom

On the lamp in the office room

On the middle shelf next to the Arachno-Gauntlet in the secret room

The locations of the ornaments in Domestic duty goes as follows
In the trash can in the kitchen

In the cabinet to the right of the dishwasher

Behind the bread box in the corner of the kitchen

In the Laundry room on the shelf

Next to the door to the garage

In the wheelbarrow

The last is under the back of the car

The locations of the ornaments in Major Inconvenience goes as follows
On the shelf under the scanner

In the Ice Cream freezer

On a shelf near the freezers

On top of the semi-truck

In the first wooden spool

In an open box next to the blue car

In the rain gutter to the left of the exit

The locations of the ornaments in Garden of Evil goes as follows
Beside the door behind you when you first load in

On the rail near the tree

Hanging on the closest cherry blossom tree

On the large rock next to the shrine

Behind the Arachno-Gauntlet

Hanging off the shrines corners

Hanging on the side of the exit

On the first food stall

On the roof overhang of the barn

On the side of the tractor

On the light over the entrance to the barn

In the hay shed across from the barn behind the support beam

Under the Assault Rifle case

On the ceiling of the barn

Under the couch of the first room

On the printer

Behind the drawing tablet

In the vending machine

In the urinal on the right in the men’s bathroom

In the second toilet from the left in women’s bathroom

On top of the projector in the conference room

In the trophy up on the shelf in the office

In the corner behind the door in the bathroom

In the mini-fridge in the hallway

On the machine on the left side of the main room

Behind the boxes next to the door to the armory

Behind the first computer in the generator room

Behind the planter to the right in the break room

On the desk on the Exterminator’s office

Behind the door to the exterminator’s office

In the Partner’s room behind the file cabinet

Behind the boxes in the hallway

Hanging from the floodlight

On top of the speaker

Hanging from the letters of the Exterminator’s building

Now I will tell you the order they come in and more about the item.
The first time you collect all of the ornaments you get the weapon “Laser Sword”
This weapon can light things on fire and is a fast melee with a fairly large range.
The second time you collect all of the ornaments you get the upgrade “Spider Noir”
This makes your screen have a noir color theme, which if you don’t know is like a black and white filter but with more grays and blacks than whites.
The third time you collect all of the ornaments you get “+10 upgrade points”
The Fourth time you collect all of the ornaments you get the upgrade “Lucky Dice”
This is an item that can be equipped onto the Tracker, its a pair of red dice.
The fifth time you collect all of the ornaments you get “+10 tracker upgrade points”
The sixth time you collect all of the ornaments you get “Low Gravity”
This is an upgrade that does exactly as it says, it makes the in-game gravity lower
The seventh time you collect all of the ornaments you get the “Radioactive wasabi flavor”
This is a cheese ball flavor that turns spiders into radioactive spider
The eighth time you collect all of the ornaments you get the weapon “Laser Gun”
This is a gun that has unlimited ammo, can light things afire and has a fairly good fire rate
The last time you collect all of the ornaments you get the upgrade “Gene Splicer”
This upgrade randomizes the spider types that spawn in a level, which can create some newer experiences